in any sort of party, the sorc is an absolute vicous whirlwind of destruction. not even my own fav, kensai sorc is necessary. any sorc, any level is going to be the best magical offensive defensive utility useful char to have in a party.
the spell selection almost doesnt matter, you can play summoner, my fav, load up on skellys, and inv stalkers and swords, summon and kill!!! use project image to override limits, and keep death fog handy for getting rid of your friends and enemies...death fog is so good...low level damage enough to allow buffed party to take freindly fire, but kills umberhulks and low level flayers, just like the death spell.
the blaster, another fav, is load up on invokation abjuration school, and use lots of spell triggers and chains to blast away at the enemy at close range...use and choose spells that get better with level, and be prepared for a blast!!!!
the generalist, prioritizes party friendly spells like mass inv and haste to make your warriors ultra powerful, and also does almost all the magical chores, like clairvoyance and farsight for mugging, and his arsenal is heavy on damage over time, in an atttempt to weaken enemy as they have to pass thru dmage zone to engage your warriors...
anyway, with a sorc pc, you dont need edwin or aerie or immie or nalia...
but a good seconary mage is good for storing spells you should not waste slots on...like reove curse or limited wish. wish is worth keeping, just for the high wisdom I gave my sorc.
a kensai sorc has some peculiar spell selection. I tried to combine all the themes I mentioned, and largly succeded, but went 6 for most levels and some levels with 7 spells...
but one of the most important spells is symbol stun, cast in chain, 1 malison then two symbol stun, set on myslef while wearing the rimg of free action is the dead stunfire spell...I plan to try out on next dragon I see...try on a high level kensai mage dual, and have fun!!!