RE: Rx/Tx suggestions
What you need to find is the old ACE Nautic Commander 5 channel Radio. It was on 75mhz and had two throttle sticks and a rudder stick with 2 additional channels. You could use the throttle sticks for steering and one of the aux channels for throttle control and the other for a start/kill switch. As far as I know they do not produce this radio any more, however you should be able to find one on the boat forums.