You have either really done your research, you've built robots before, or you're a complete natural! All the right stuff going through your mind by the looks of it, with solid components and you're clearly comfortable in CAD... is that OnShape?

Big drum+4WD is an extremely popular and successful shape in American insects through 6kg bots. These both happen to be hubmotor drums, but for example: http://3.bp.blogspot.com/-DipBqGVjqz...217_144935.jpg - these are both formidable.

I would push for invertability, at least such that you can drive to some extent (so's not to get counted out) when inverted.

As Harry says, really looking forward seeing what you do!