legacy

Surely you jest. This is not Alabama or Auburn. Women are not knocking down the doors and begging us to pledge them. Hell, most students don't even know there are sororities and fraternities at UAB.
It's entirely possible to pledge a sorority as a sophomore...or a junior, or even a senior. This is the land of the non-traditional student, so you're fine.
I have no idea of AOPi will affiliate you or not; sorry, not my sorority. But I'd bet the would.

You wouldn't be "affiliated" because you aren't a member. Being a legacy is not the same as being a member. Go through recruitment and see where you fit in best. AOII may like you and they may not. Legacy status is no guarantee of anything, but UAB is not terribly competitive. Being a sophomore shouldn't hurt you too much. Good luck!