Buy as much radio as you can afford if you think you will stay with the hobby. If not it really doesn't matter. Having a radio with exponential really helps the beginner with the tendency to overcontrol as it softens the control feel around center. Particularly useful on landing. Look at the Hitec radios as they give more for the money invested. The receivers are compatable with Futaba if you get a better radio (transmitter) later and the servos can be used as well.

A buddy box is a second transmitter that is linked by a cable to the transmitting radio. Control is given to the student and can be taken back when the student gets into trouble. The problem with some buddy box systems is the main transmitter may have expo however the buddy box doesn't which makes it bad for the student. I fly a computer radio and the buddy box just gives the control inputs to the student. All mixes and settings come from the transmitting radio.

All the plane choices you had in the orignal post are good ones. I would recommend a larger craft however as the smaller "tail draggers" can be a handful on the ground. I did have one student with the 20 size cub and it is a rather large plane for the size engine. It would fly for half an hour on 4 oz of fuel.

EXCAP232