Dual fighter/arcane caster advice

So the first charname i actually managed to stay interested in long enough to beat the game with is a fighter focusing on greatswords and fiddling with crossbows, but has always had an interest in the arcane arts. Gorions death put a bad taste in her mouth about learning magic, but interacting with Neera and Xan and overcoming the final trials of BG1 convinvce her to look back into it blah blah blah.

So where i need advice is what level should i get to before dual-ing? A cursory glance at the exp chart makes me think its not worth trying to fit in the second class during the first game, and that level nine seems the most obvious choice to get the most HP. What else is there to consider?

Then i am still torn between mage and sorc. I always kean towards mage because i like the feeling of a well planned memorization working out, but the extra spells per day are very appealing, even if it doesnt fit the backstory as well.

Any suggestions and discussion very welcome and appreciated!