Possible SPOILERS below
@Mortal : Keldorn and Viconia will fight... eventually... so it isn't a great Idea to have both in your party.
@Incertainty :
Yoshimo is part of the story... that's my reason from bringing him. The exp gained this way is only a little bonus. Yoshimo brings a new alternative route to enter spellhold (the "I'm crazy" one). When I don't want to play with him, I just keep my 6th character slot empty, because I don't like to drop a character in spellhold to recover Imoen. I have, too, over-used jan, so I enjoy going to Brynnlaw with Yoshimo in my party.
Nalia will do fine as a mage. I believe she can reach the same level as edwin (but she doesn't get the +2 spell/spell level bonus because of Edwin being a Thayvian Wizard (Thayvian Amulet + Specialist), so she will have fewer spells). Anyway, being a dualclassed thief/mage makes her able to use short bows, wich is a good advantage. She will also progress pretty fast as a Mage, gaining access to higher level spells quickly, unlike Aerie and Jan Jansen. The only thing I don't like about nalia, is that she's a pale copy of Imoen (Imoen being a decent thief at least, while nalia doesn't have enough skills). You might want to choose Edwin for this reason, and since he's a great mage, he could be useful (he'll always have more spells than any other mages in the game, that's for sure!).
Minsc will do good job as a Tank. Good damage-dealer/receiver, he's your best bet. Before though combat, use his low-level druidics spells (gained from being a Ranger) such as Armor of Faith (10-15% bonus to physical resistance can be a life-saver) and Remove Fear.
The PC choice is good (Fighter/Mage), but if you plan to go through Shadow of Amn only, you might want to try out a dual-classed character, since low levels (roughtly lvl 1 to 10) needs only a bit of exp to level up. A Fighter dual classed to a mage at level 9 (Profiency point gained, no more hit points dices after lvl 9) will be a real killed. You could also add a kit for a greater result (Berserker will give you various immunities/bonus while raging, while a Kensai is a real killing machine, and combine well since a Fighter/Mage won't wear armors anyway (this dual-class can still wear robes!).)
1/ By the way, does anyone know an xp-cap remover? 2/ How do strongholds work for multi-/dual-class? Do they get 2? 3 maybe
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?
1. Do a quick search for either Baldurdash or Ease-Of-Use mod. These two will add an xp-cap remover.
2. You only get one, unless you install a mod that change this rule (Ease of Use changes it
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). You get only the first one you accept! (There's a bug involving the fighter and the mage stronghold... wich you can pick both. not sure how it's working though).
Good luck!