You can run all the motors on one side from the same (side of a, for dual channel* controllers) speed controller, so you don't need a separate radio channel for each motor! The speed controller will drive the motors forwards and backwards from just one radio channel, so the bare minimum you'll need is three - two channels for drive and one for weapon. The drive channels are often 'mixed' to give forwards/backwards/left/right control on one joystick; this function can be done in the radio transmitter, in most dual channel speed controllers, or a separate device known as a 'mixer' in the robot between the radio reciever and speed controller(s).

All the sets you linked will work; the key thing for combat robotics is that the reciever failsafes properly (to avoid a runaway robot). I use odd radio gear myself, so I'll leave specific recommendations up to others, but it can come largely down to personal preference, and it's not something you need to worry too much about committing to too heavily as it's completely swappable.

*try not to get too confused between 'channels' on speed controllers and radio gear. it does happen. :P