If you have access to a lathe then the best recommendation for wheels i have is to make your own hub and screw bike tyre around the outside.

For the RX i use the Spektrum AR610 DSMX 6 Channel Receiver, ill be honest its not the cheapest option - and theres RXs 3 times less which do the job just as well, but since i use a Spektrum TX i just prefer the peace of mind it offers me (and £20 isnt much in the scheme of things)

Transmitter id go for Spektrum DX6i - its the right blend of cost, function, and capacity.

Armour really depends on what you can do. Scoops are best made of metal, preferably a hardened steel - though your chassis can be made of a blend of Ranglebox threaded bar (your welcome Ellis) and HDPE

Only additional i notice is theres no point in an on/off switch - its only likely to get accidentally triggered and the link by regulation serves that function.

Theres also a few tiny things, like the + and - tend to come out the same side of the battery. And the drivetrain is a bit to cramped, but realistically given the stage of design your at its not a problem, just want to make you aware as you go forwards to a more detailed design.