The wall wart referenced has dual circuits in it, one for the receiver and the other for the transmitter. Your tank chargers will not work. As far as why you need seven channels, the answer is that you do not need seven channels for this airplane, but if you intend to have more airplanes in future, you will eventually need more than four channels. The one item in this hobby that will stay with you for a long time is your radio system. Airplanes, engines, etc., will come and go, but your radio will stay with you. This is the single item that you need to get the best you can possibly afford/justify right from the git_go.