Does party size affect the number of enemies you face? If I tell the Blade/Bard and Jaheira to leave my party will I be able to get them back later in the game? Right now I have a 6 person party but I want to dump Jaheira and the Bard so I can travel with 4...this way I level up faster right?
Then only thing that affects the number/type of enemies is your level. Party size does not directly affect this (Although you will level up quicker with less people, so you will face harder enemies sooner).
You do get more experience per party member if you have a smaller party, true. One cheesy tactic for a player dual class mage is to drop all party members after dualing from another class (typically some kind of fighter), then learning spells. Usually, you can gain up to nine levels that way.
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IMO your best off with 5 Members (yourself included) or 4 if your main guy is at least a decent fighter.This for single player.
For Multi player, you could probably cram it into 3 well made characters.
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