Some of the best RC trainers have only three channels. Rudder, elevator and throttle. Best example the Sig Kadet Senior. As mentioned before get the best radio you can afford without mortgaging the house. 4 channel if you have to, 6 channel if you can. Gas engines are usually quite large and heavy and are meant fot at least 1/4 scale. Glow engines can run up to 1.5 inches but the most common sizes run from .25 to .60 and the range of trainers that use those sizes is amazing. Just look in almost any model magazine for a trainer that appeals to you, or better still find out what the pilots at your field have to recommend. All engines in common use have throttle control except the Cox reed valves and even some of them have throttle control. Electric motors are usually used with an ESC (electronic speed control) which is just another name for a throttle.