Nobody has yet found a need for a diagram for a 2 channel setup.
If you stick to one manufacturer for your parts, the battery will plug into a switch harness and almost nowhere else because of the shape of the plug and socket. The switch harness or the battery will plug into a hole in the RX usually marked "B". The TX will have sticks probably marked with channel numbers, and the RX will have channels similarly numbered, that the other bits plug into. It is rather simpler than Lego(TM), there being less choices.
Places like Servo Shop, Component Shop and Howes have a good range of servos, including the micro types that will be OK for your rudder and whatever you choose for sail control. No clues there, don't know what space you have, what weight you can stand, or how much sail you want to handle in what conditions.