Looking good!
How thick of alum. are you going to use for the chassis?
Have you figured how you're going to secure your battery packs?

A couple suggestions:
Add a milled slot to each end and on each side of the battery locations, in case you decide to use web straps to secure them. Easier for your buddy to mill them in (even if you never use them) than to want them later and not have them.

If you're going to use rigid straps mounted on posts, drilling holes is no big deal - slots aren't as easy!

Might also suggest making the chassis out of thicker stock (perhaps 5 or 6mm) and plan on milling down the majority of it to perhaps 3 or 4mm. I.e., leave a 3 or 4mm wide "lip" all around, for increased rigidity. Leave chassis full thickness over mounting points.
Easy for your buddy to do, if he's using CNC milling equipment - and will leave folk's jaws on the floor when they see the finished product! :004:

good luck and take lots of pics!