Even to have an on/off switch you still need a channel on the Tx to switch it. Just having a manual On switch and letting the motor run until the battery goes flat is not a good idea. When the battery runs low on power the plane comes down and unless you have landing gear it stalls the prop and either burns the motor out or damages the gearing.

Anyway you can't run the Rx and servos direct off a 7 cell motor pack or you'll kill them and carrying a motor pack and a 4-cell Rx pack would add too much weight again. A speed controller will have a BEC feature which reduces the voltage from the motor pack to a suitable level.

What flight controls are you using ? Elevator I guess but are you going for rudder or ailerons ? Ailerons work better on low wing planes without much dihedral but they're trickier to build and set up.

You may be better making a static model. Mounted on a nice plinth with a working prop and wiggling controls it would be quite cute.

Good luck anyway. I'm afraid you might be needing it.

Steve