I would start in BG1 if only just to get use to playing a mage, because IMHO a mage is easest to start in BG1. I would go with a mage/cleark or a mage of a pacific school for the extra spells wich can determin life and death of the mage.
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All blades cut, be they made from metal or wood, but the sharpest and deadliest blade is the one of knowledge.
An Archmage of the HADB