Very nice work.
6061 is strong but bends and scratches too easy. 7075 is an ideal choice for the chassis. 7075 costs a little more but is worth the money in the long run.
I am using Lipo's as well so i made myself a custom bottom plate without cutouts for the batts. This was to protect my Lipo's from getting puntured from below. This might be something to consider for the future. The solid bottom plate around the batts adds some ounces but helps me feel better about the abuse I'm putting them through.
