hey matthew, You do not need 3 sets of crystals but it is advisable incase of any clashes. They are usualy around £6 a set and controls will need to be bought. If you are looking at buying a controller set then you will already have a set of crystals with it. not worth splashing out on some more until you are going to an event. Contact James cooper From Robo-Challenge/Rc Wars if you are looking for cheap controllers, speed controllers or any other electrical components. When you get to the wheel stage, he sells extreamely good wheels for extreamly low prices as he makes them!
Good Luck