RE: Slow stick batteries
I answered most of this post in the batteries forum.
You are correct in your understanding. The main battery on the airplane powers both the receiver/servos, and the motor. This is done through a regulator circuit on the speed control called a BEC, battery eliminator circuit. For applications up to 10 cells, you will almost always use the BEC feature of the speed control to simplify things and save weight. Batteries over 10 cells have too high a voltage for the cheap BEC chips to regulate, so you normally have to disable the BEC and use a normal receiver pack or an Ultimate BEC (separate product).