Hello Peter,

As far as radio is concerned, 40Mhz is the only option, as long as the Spektrums are not legal yet, and for a rambot you can make do with 2 channels (forward/backward 1 channel, left right the other), but if in a later stage you want to make a remote controlled weapon, a third channel would be needed, so its better to start off with 4 channels so you are set for the future.

As for speed control, there are various flavors, all in different priceranges. The best in my opinion are the sidewinder and the mini vantec, but Electronize and Mtronik also are very nice.

As for power, you can go to obscene amounts of power in a rambot, but if you cant get that power to the floor, it is of no use. So make sure you get some good wheels to match the drive train you want. James already posted some good expamples.

Have fun building and battling.