RE: 4ch or 6ch?
Well, I'm gonna buck what Aeajr has to say. I usually don't recommend that student learning to fly get a computer radio. I have nothing against them having the computer radio, but in all reality it's hard for anybody to not play with all the "bells and whistles" of the radio. And a student doesn't need those bells and whistles. A student needs to learn to fly the plane. Plain and simple. They can't learn to fly a plane if the radio is doing mixes and other features that a computer radio offers. For this reason I usually like to see new pilots on a basic 4/6 channel radio. If they can get the computer radio and not use any of the fancy extras from that radio then that is fine too. But that does take a lot of self control on the part of the student, but they will be a better pilot in the end of they can avoid doing this.
I own 3 computer radios and I do use some of the features that are available, but I try to resist if I can. Why?? Because I think that I am a better pilot if I avoid relying on the radio instead of skill. For example, I used to have an aileron/rudder mix on my radios that I would use when I was making a crosswind landing. I got to where I could make those landing pretty good like that. Then a flying buddy challenged me to do it without the computer radio. I couldn't do it. No matter how hard I tried. So I started practicing manually using the rudder on a crosswind landing. I've gotten my landing down now without relying on the radio. And the landings are so much better than I could ever do with the radio mixing. Why?? Because I have a feel for what the plane is actually doing, I'm flying the plane instead of the radio doing it for me. And that "feel" has helped me in a lot of my other aerobatic maneuvers. The loop for instance. Some feel that the loop is a simple trick to do. But do it in a crosswind. Because of my time on the rudder stick in landings my left thumb knows exactly what to do in a loop during a crosswind to keep the loop tracking straight. It helps almost all of my flying.
So to sum it all up. Learn to fly and don't rely on the radio as a crutch. You'll be a better pilot because of it. I do urge pilots to take advantage of the features of a computer radio, but after they can fly the plane without it.
That's my 2ยข worth.
Ken