On motors, batteries and speedos. First of all, they wont come cheap if you buy new.

One stop shop for the starting roboteer is http://www.technobots.co.ukwww.technobots.co.uk

Paul Cooper is a roboteer ,and knows exactly what you can use.

What we (team RCC) use. Sidewinder speedos are very much the favorite in the heavies. Affordable, small and powerfull enough for a normal drivetrain.

Spectrum 2.4GHz RX/TX with of course the BR6000 robot wars specific reciever.

3700mAh NiMH GP 12V batterypacks

Motors, we used Bosch 750s, starter motors littons and the AEG Bosch 750 equivalent. But now were building an experimental drive....

Wheelsize. I did build 2 drivetrains were the Bosch 750motor was in the wheel. And the wheel was only 200mm outside diameter. So, its possible.