The main rule was that you were only supposed to take the NPC's who were required for the game (Dyson Leland and Overdune Snapfinger). These NPC's were not to be used in combat nor could they cast any spells. "Fast" Freddy Talimere can also be bypassed, but I don't want to give you a full spoiler as to how that works. 
As for which class to take, Dark Elf, Knight and Necro were the ones most highly suggested for such an adventure, back in the day. Trolls and Clerics are reasonable (but diffuclt) alternatives. Minotaurs and Vampires aren't well geared to solo adventures. I'm one of a very few here who like Vampires, but I acknoweledge that they do best as supporting cast members.
Good luck.
