RE: EP glider questions
The fist thing to do is read the instructions. The mfg usually recommends battery sizes. Weight will be a mjor factor, especially when you go to balance the plane, a step you generally can skip with cars.
A car speed control might work but I would go with a plane speed control as most have a BEC, battery elimination circut. Not sure if this is common with cars. This allows the receiver to be run off of the flight battery.
Most airplane ESC/BEC have a cut off for the motor so when the battery gets too low, it will cut off the motor but leave enough power to keep the radio equipment running so you can land the plane.