As for mountaineering and pathfinding, this is something you`ll have to live with, heh! However, in MM4+5 Rangers can use the Jump spell, and that helps a lot in the forests.... Also, items of Teleportation and Etheralization are invaluable tools. Another thing to consider is that once up in the mountain, you can often keep walking without teleporting/etheralizing further. This won`t always be the case, though.

Certainly, Archers/Sorcerers have an advntage with the teleport and etheralize spells, whereas Paladins/Clerics has the top healing spells. However, you won`t need resurrection, flesh to stone or raise dead in a solo game, thus my recommendation is the ranger, for the enhanced combat abilities over the Druid.

It`ll be interesting to know how you fare and what character you end up choosing.

Keep us posted and Good luck!