1. Not a problem for something like a trainer. If you were into Pattern then you would a little concerned
2. Yes. Throttle down low. You will need to break in engine if it is new.
3. Ch 1 = Ailerons, Ch 2 = Elevator, Ch 3 = Throttle, Ch 4 = Rudder

Get hooked up with a club and an experienced trainer. You will save yourself a lot of heartache and money that way. I can't stress this enough. Starting and engine is a lot more complicated than what I can explain here without more information (type of engine, etc). You also need to have someone experience to make sure the radio/servos are set up properly.

Again, get in a club, find an experienced pilot to train you, and join AMA if you haven't already.