Sorry Weeds, but you do have quite a bit to learn about electricity, the parts that control it, and what happens when you exceed the power ratings. A "volume knob resistor" has a totally inappropriate value of resistance for directly controlling a motor, and a totally inadequate power rating. The model boating description would be "One time smoke generator".
No reverse. Reverse on a boat is your brakes. It is also how you back away from trouble. If all that is wanted is the same, or less, control than that supplied by the original, you have a good plan. Normally the idea of converting an RTR is to UPgrade the controls to be equivalent to a normal model.
Its not April fools day is it.
Either very early, or very late.