Mana trains do not allow you to cast more spells, except in so far as they provide you more mana to do so with. Your concentration limit is determined by your INT score, and INT score alone, and your concentration limit is what limits the number and type of spells you can cast/hold at the same time.
Polymorph changes only your race and adj. In fact, you can polymorph into non-PC races as well. Since your aura is determined by your alignment, and that is not changed by polymorph, no, you won't appear to be a light aura if you poly to an elf from a deep-elf.
Polymorph doesn't change your eq sizes. However, as a sorc, you have enlarge/shrink spells which will accomplish the task with very little time or effort required.
It's not the casting time of flight that's the problem. It's the fact that being under the affect magical flight raises the casting time of all your other spells. It also makes you take a penalty to your evasion. For example:
Quote:
o Affect: 'fly' - penalty to casting time o
o Affect: 'fly' - penalty to probability to dodge o
o Affect: 'fly' - penalty to weapon accuracy o