If you were only playing BG2, you should have chosen Sorcerer, since sorcerers are FAR superior compared to the mages, but if you want to play from BG1, I sould suggest either a Cleric/Mage, a Fighter/Mage or a Mage/Thief, all of them get better THAC0 and more weapons to choose from from their non-mage class, unfortunately, Robes of the Archmagi are VERY rare and VERY expensive in BG1 and there's neither Elven Chain or Elven Plate, so you probably won't get to use it unless the enemy ambushes you are gets through your fighters, remember to choose Elf as your race so you can have 19 Dex from the beginning, otherwise a mage character is dead from the first chapter.
Invaluable NPC allies:
BG1:
Minsc, the perfect warrior, can be found in Nashkel.
Kivan a ranger, can be found west of Beregost.
Khalid and Jaheira, can be found in the Friendly Arm Inn.
Imoen, you need a thief, can be found just outside of Candlekeep.
BG2:
Minsc, for fun, is with you from the start.
Jaheira, she's useful, with you from the start.
Aerie, Cleric/Mage, one of the strongest characters in the game, even if she is a bit annoying at times, can be found in the circus tent outside of the first dungeon.
Jan, the only decent NPC thief in BG2, can be found in the Government District.
For your last NPC, I would suggest either:
Imoen, for storyline.
Anoment, Fighter/Cleric.
Keldorn, Paladin Kit.
Valygar, Stalker, Ranger Kit.
Mazzy, Halfling Fighter.
Korgan, a good fighter, he's evil though.
or
Edwin, the only pure NPC mage in ToB, he's pretty damn good too, unfortunately he's evil.
BG2: ToB
Only one new NPC here, switch one of your NPC's from BG2 for him, he's THE best fighter in the game, he has skills that even PC fighters cannot acquire, I suggest that you switch your last NPC(One from the long list at the end of my BG2 NPC suggestions.) for him, he's worth it.
And remember one thing when playing a mage, Magic Missile is THE most useful spell in the game.
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Wielder of the ancient Lawyer spells.
Member of the HADB clan.
Ally of the Fluffy Queen and the Dreaded Red Fluffy
General of the highest class and Leader of in the IW Peacekeeping Force.
ORT member, Official Demander of Stuff.
Sorcerer of Lady Lioness's Court.
1 point from sainthood in the test of corruption.
2nd place in the longest sig of IW contest 2001.
"If Silence is golden, why does everyone talk so much?"