Since the quilt is going to Alabama (and it's hot) I'd suggest a wool batting. Wool breathes and is perfect for southern or summer quilts. It wouldn't need to be black. Just be warned: when wet it will smell like a wet....sheep.
As for the batting size - check with the quilter. We all have our individual requirements. I prefer 4" extra all the way around for both the back and batting. That said, most of my customers buy the batting from me, and I just cut what I need off the roll.