[Minerva]

Multi class in BG1 is very tough, especially if you pick one with non-warrior classes due to low hit point and slow level up. I once made a half-elf mage/cleric, and was really difficult to keep her alive, especially during the first three chapters.
The reward was great, though. I created her because I wanted to take her all the way to ToB, and thanks to those tomes and good roll of dice (I had total of 94 or something ater re-rolled 3times), she even had decent strength to melee (and I never created a character with too low charisma either. She had 13 without any equipment).
It depends on your play style and who you are going to take with, but cleric with mage or thief would definitely give you challenge and they are nice choice in SoA (well, at least I didn't need Anomen in my party).

As for the quests, it is the same as you have created multi-class character in SoA as Stilgar says. So you can do only one class specific quest, unless you install a multi-stronghold mod.