1 How many NPCs do you usually include (for solo, 0)?
Five at any given time, though my party composition changes over the course of the game.
2 Do you prefer a themed party (all good, all evil, all mages, all wizard slayers, etc.) or do you prefer a balanced party in terms of class and alignment?
Balanced in terms of class, but balanced in terms of alignment is kind of impossible in BG, and probably would be tough to roleplay with most character concepts.
3 Does NPC personality influence your party composition?
It's my number one influence.
4 Does an NPC quest influence you party composition?
Yes, I pick up NPCs for their quests even if I don't keep them in my party long-term.
5 Does NPC power influence your party composition?
6 Regarding your PC (player 1), do you single-class, dual-, or multi-?
Yes. . I don't play the same character every time.
7 How powerful do you want your PC to be in terms of the challenges posed by the game?
Powerful enough to be challenged by them but not destroyed by them. I don't like mods that add incredibly tough battles, especially those that only have one strategy to win.
8 How powerful do you want your PC to be compared to the NPCs?
Slightly more powerful, as the PC's stats are rolled, and she is the child of a god. NPCs with similar stats should be extremely rare, like Sarevok.
9 How do you utilize multi-classed characters?
I'm not sure I completely understand this question, but I'll give it a shot. I don't equip anything on them that would disable any of their abilities, and I use all their abilities. Jaheira spends as much time doing fighter stuff as doing druid stuff, Aerie casts as many mage spells as cleric spells (if rest-casting isn't counted), etc.
10 How do you use 'specialty-class' characters (bards, monks, specialty kits)?
I don't really get this question either. I just use all their abilities, when appropriate.