I think i will move on to MM7 and 8 soon, how much of my experience from MM6 will apply to those game and could someone perhaps provide me with a short area progression/start up guide like this one?

General and Party creation:
1. The game is not so hard that you NEED to make any given choices, in fact optimal groups are almost too powerful. Still, it's nice to know what you can choose and why, and this guide gives some idea of that.
2. water magic gives you Lloyd's beacon which allows you to heal life and mana to full in a few minutes because you can teleport to the temple and back in about a minute. Not getting water magic will mean A LOT of downtime and the game has plenty of that even with Beacon. Master water magic is preferable, expert sufficient.
Beacon also lets you buff yourself at the +30 levels well at Kriegspire (+50-100% to life and mana total), you can also get increased stats at other wells/fountains but stats have diminishing returns, so far less benefit.
3. Early game you will deal 2-3 times the damage if you have access to bless and heroism, either be sure to use potions for these effects, or, alternatively, one guy with expert spirit is a good investment. Midgame light magic gives you hour of power which increases damage even more. Parties relying on weapons for damage will deal about 30% the damage without these buff spells.
4. Only use turnbased mode to fight if you have trouble pressing 'c' to choose spells or enemies cant reach you. Running parallel to ranged enemies will make them miss most attacks, when all characters are ready turn and fire a volley (spells or weapons) while running. Against melee run away, turn for volley, turn and run again (moving backwards enemies will catch up, they wont if you alternate running and shooting). Similarly use corners for cover while "reloading", pop out to draw fire, hide, then as missiles fly past pop out and loose volley. Same for melee, although avoiding damage entirely is rarely possible at melee range.
5. Investing all your points in a single magic skill will get you about 40% higher skill level (and thus damage) than spreading them over two skills and 80% higher than 3 skills. At end of game you will usually be level 50-100 depending how much you skip, this means around 500-1000 skillpoints - dont be afraid to divesify, especially to master skills you use often. Weapon skills have low return on skill points and dont need to be raised over master level (8), unless you have no better alternatives (knights)
6. For followers choose a merchant and duper, together they will triple your golds' worth, double that if you get a guy with expert merchant. Replace them when you've bought the spells and mastered the skills you want. For midgame onwards teacher/instructor, Mystic/spell master or healers are your best choices. I prefer Mystic/spell master.
7. "Utility" or noncombat skills: you need a guy with disarm and perception at rank 1 early as possible, and its a good idea to get to rank 4/expert before you start on you combat skills. Preferably get someone with expert identify and repair as well.
8. Classes in MM6 are about what combat skills the character has access to and there's a lot of overlapping. If a class has access to a skill he can become just as skilled at that skill as any other class. This means sorcerers/cleric can become as powrful fighters as knights.
Weapon: Needs magic buffs to be efficient, doesnt rely on mana, so no downtime till you run out of life. which happens faster than efficient casters run out of mana.
Self (body/spirit/mind): Bad damage spells, lot of utility spells like curing debuffs, buffing and healing. You only need expert (rank 4) in these schools to get full effect, further skill points are mostly wasted. The exception is body magic that has the one good healing spell in the game, power cure, with excellent return on point investment (8 pr point). Together with shared life from spirit (which has bad return on investment, but is extremely efficient even at rank 1)) Body magic can give you an efficient healer.
Elemental: Bad-mediocre damage spells (damage output about the same as buffed weaponskills except when AOEing many targets), great utility. Some AOE combat spells work great even at rank 1 or 4+expert: starburst, inferno, fireblast. Fire has good AOE spells but the final dungeon almost every demon is immune to fire, Water has great traveling spells, Air has Flying and jump. Earth has frustrating spells that cost too much and doesn't autoaim.
Dark magic: Shrap metal deals many times the damage of weapons and elemental magic (the dark magic poison spells+finger have their use as well), elemental starts out pretty decent but mid-late game runs into high resistances/immunities.
Light magic: Powerful buffs for weapondamage, a few good damage spells for specific enemies like destroy undead and prismatic light. Don't bother with more than a few points in this for a party that rarely uses weapons.
Shrap metal deals up to 24,5 pr skill and about 0,5 pr mana (pr skill), while elemental spells deal about 4 pr skill, at about same manaefficiency. If you factor in damagetype where physical deals with fewer immunities and resistances than the others, shrap metal is even better. Without beacon they'd be more or less equally good, with beacon and the infinite mana it brings shrap metal is clearly better.
9. Spells you will want/use
Shrap metal(dark): best damage spell. you barely need any other
Lloyds beacon/town portal(water): teleports you to places that give you buff and healing
Day of protection(dark): makes all nonphysical attacks deal a fraction of normal damage.
Power cure (body): heals entire party, master body magic and moving will keep your party in good health against just about any enemy. You can make do without it but will need a lot of hit and run.
Shared life (body): just needs rank 1 spirit magic, little benefit from further points. redistributes life among party
Fly and jump: some quests cant be done without these, many dungeons are much longer/harder without jump

Optional:
inferno/ring of fire (fire): best AOE spells, against 10-20 enemies these are even better than shrap metal. They can make the early game almost too easy (and castle darkmoor much easier than it is without them), and can occasionally be used effectively all the way up to the final dungeon where almost all enemies are immune to fire.
Prismatic light (light): another great AOE spell, many are immune to the magic damage it deals however
Hour of power (light): Incredible boost to weapondamage. If you rely on weapons this spell is a must, and worth ranking light magic for.
Day of the gods (light): nice boost to stats

The other spells are redundant because of shrap metal being so powerful, a few like star burst/meteor shower/mass distortion will occasionally be useful, but you dont need them.

10. The classes are:
cleric/sorcerer who have access to dark magic (and light), as well as self/elemental. The most efficient party has mostly or only these classes.
Archer/Paladin/Druid: Only access to elemental (archer+druid) or self (paladin+druid), but not dark/light. Archer and Paladin also have more life and less mana than cleric/sorcerer. There's little reason to include these but you can do so to have a character act as utilityguy, fx a druid to act as beacon and healer, allowing the others to focus fully on specializing dark magic.
Knight: Almost 3 times as much life as cleric/sorcerer/druid. Replacing a caster with a knight will (guesstimate) give your party +40% life and -15% damage, across the game (same damage for first part, barely contributing in last part of the game). However master body magic will add much more life to your party and if a cleric also running darkmagic will cost much less damage.
11. Having a character skill body magic alongside an offensive skill, preferably dark magic is not required but advisable, a single healer will triple your parties life.
If you aren't overly concerned with maximum efficiency and want a bit of a challenge you can create parties without dark magic, but as mentioned, dark magic deals 2-3 times as much damage. Late game is slow going without at least 2 dark magic users.
If you go with weaponbased party, spirit and later light magic is strongly recommended, as well as water (which means the most knights you'd want is 3 knights + 1 sorcerer although 4 knights is possible even if their damage is very low).
Personally I enjoyed my archer heavy party with each guy leveling an elemental school and the all healer/melee party. Perhaps even more than the dark(+fire) magic group who simply tore through the enemies.
12. Skill progression: Your first priority should be getting one character to expert in spirit, disarm, identify, perception, repair. Then get your combat skill to master, then master the nonmagic utility skills, get expert identify and repair for all your guys, get master meditation and bodybuilding, finally getting your combat skills as high as possible.
Learning should be your first major purchase, it is very efficient at rank 1, but doesnt give you much for ranking it higher.

13. Early game:
a few ways to raise your level and fill your purse before starting the game in earnest:
NWC dungeon gets you 10k+ gold as many times as you like
A gatemaster follower can get you to the big cities to loot horseshoes and get highpowered weapons at relatively low cost, particularly spears at blackshire and bows at frozen highland.
At Free haven there's a cavalier quest that can be done at level 1 aand gets you to level 6.
Loretta Fleise in silver cove gives a price fixing quest that can easily be done at level 1 with a gate master follower (or 2)
Guy in tavern at new sorpigal will give you 1000 gold and taking the letter to Ironfist gets you another 5000 gold and 2 levels.
I usually just do the last one (letter then coach to ironfist), the others seem more than a little like cheating and take long, whereas i'd usually be going to ironfist anyway to learn bow. Get your guys +4 bows and set out:

A. Clear new sorpigal mainland and the two dungeons, islands are optional with the fly scroll. Be sure to have bless and preferably heroism up at all times
B. clear temple of baa. Step A and B can be done with rank 1 in bows and melee weapon.
C. get to Free haven (run N-E of ironfist map or hire with a gatemaster follower), do cavalier quest if you haven't already. travel north on western part of map to castle stone and get prince of thieves and cleric quest. Clear sewer and restore temple. Optional: clear islands near Mist.
I prefer to feed all the horseshoes (found at stables, give 2 skillpoints) to a guy with water magic and have master level town portal up and running from level 12.
At this point there are a lot of easy council quests:
http://www.mightandmagicwalkthrough.com/mightandmagic6/477-find-lord-kilburns-shield.html
http://www.mightandmagicwalkthrough.com/mightandmagic6/479-end-winter.html / http://www.mightandmagicwalkthrough.com/mightandmagic6/89-high-council-quest-stromgard-winter-stoppage.html
http://www.mightandmagicwalkthrough.com/mightandmagic6/83-high-council-loretta-fleise-price-fixing.html
http://www.mightandmagicwalkthrough.com/mightandmagic6/478-destroy-the-devils-outpost.html

The first three can be done just by using fly/town portal, even at level 1. The devil's outpost requires a little fighting but you just need to kill 1 devil, a red bastard that comes from the left and pick up the scroll he drops when you kill him.
In total these 4 quests will give you almost 200000 XP, enough to reach level 20-28 depending on when you start them. Doing these quests at this juncture, or even earlier means effectively skipping early or midgame though, so you may want to only do these (indeed any) quests after you kill all enemies in the low level areas up to and including blackshire.

D. class quests for your party, you can do the other class quests as well for XP but more importantly the class quests are a huge boost to life/mana when you have the class.

If you do the council quests early you can go directly to endgame if you wish. Personally i prefer to clear all dungeons, this is the order of difficulty:
E. Dungeons around ironfist, bootleg bay, mist, superior temple of baa (only the dungeon) and frozen highland (dungeon only, archers and magyars later). Finish this step with Corlagon's estate.
E. Clear silver cove and blackshire, supreme temple of baa, mire of the damned
F. Castle alamos and castle darkmoor
F clear Kriegspire
G Tomb of varn then control center
G clear dragonsand, sweetwater and Paradise valley
H. The hive. (final dungeon

Y. a few spots with free kills:
in the big room in temple of baa hundreds of skeletons will appear once you mount the dais. the secret door behind the altar leads to balconies from where you can shoot at the skeletons from perfect safety.
in Nergle's iron mines there's a lift into a room with many enemies, rousing them then descending with lift will bring them to you but only bats can reach you.
in hall of the Firelord main, large room, run down one of the two holes and look up to shoot the monsters gathering around.
in icewing keep lure the monsters to the locked gate across from entrance, you can attack through the hole but they cant attack back.
casting armageddon in kriegspire (you need enough to kill the monsters there) will net you as much as 150000 xp and gold if you have used the +30 level well often (each time dragons spawn to the north-east). You can use armageddon on other maps as well but will kill civilians in many of them and net 10-20%. I like to "make the rounds" once i get master light (using followers to gain reputation), in order to get bad enough reputation to get master dark magic.

Fixing MM6
As such the game works however I'd want the following issues fixed if I could:
Dark magic, particularly shrap metal is far more powerful than any other spell in the game.In my opinion other attacks are too weak and shrap metal too powerful.
Too many immune or near immune monsters for elemental and magic damagespells
Lloyd's beacon is pretty much a must.
knights have 0 abilities
weapon skills arent good enough to rank high
too many useless spells