If he goes higher on the weapon he may damage the drive. Its the same issue you would have had. Split voltage is always an option but that means 2 links and more complex wiring.

As a rule of thumb your robots wheel base should be wider than it is longer as it helps turning and reduces scrubbing, square at maximum. If you can do that then go for it.

The robot looks fairly simple, just very sturdily built. You may have issues getting your drive motors in and out but its just inherent in the design.