What is the difference of 3 channel and a 4 channel plane?

I know there are certain "flaps" on planes what are they called and where are they located?

What is up with the Trasmitters, recievers, and servos? Can someone define those to me and recommend some to me?

I hear a lot of talk about engine size, (electric) 280, 380, and 400 which one is more powerful? 400?

I think i am going to pick up the "T-hawk" what would be a good RC controller for it?

http://www.readytoflyfun.com/thawk3chrtf.html

A lot of people that I have spoke to in these forums think I should not start out with a park flyer, but to be honest i think that is all the plane i want. The T-hawk is a 3 channel RC plane would that be a problem if i was to purchase a 4 maybe 5 channel radio and use it for the t hawk and still be able to use that radio for my next plane? If so, which radio would you guys recommend?

Any help is appreiciated