Want a simple test frame, and don't want to take apart your robot too much? Use 3/4" ply and mount your wheels via pieces of channel into cut outs. You can just screw down the toughboxes with the standard mounting hardware. The bonus of plywood is that it will help keep even weight distribution on all your wheels because of its flexibility.
I think everybody else covered the tech requirements, but make sure you have someone willing to program it, or it
will be a pain to deal with. I am sure you won't be convinced until you have built it yourself (because I was the same way
), but a 6/8WD done after some research on CD and careful design is the best drive train for FRC (you can always make modifications to make it work better for the game at hand).