You asked what radio you should get.....I come from a different line of thinking than was posted above....
It's an easy question to ask....but very difficult to answer.....first off you'll probably never get half your money back selling used equipment so ask yourself some basic questions.....If you were to crash your new airplane on it's maiden flight...would get a new airplane and begin again...or walk away? If the answer is a new plane and you're sure that this is the hobby for you.....then get the biggest baddest radio you can afford.....if you might walk away.... then perhaps something smaller until you know what your future is in our great hobby.
Here's what I'm thinking....in the long run it's cheaper to get a big radio now than later.....it's also cheaper to get a big radio now than a small radio now and a bigger radio later....
I know you're probably saying as I did that you can't ever see using more than 6 channels.....If down the road you get into larger airplanes like gassers...you can eat channels pretty quickly....like 2 channels for aileron and 2 for elevator...there's 4 rudder makes 5 battery 6, throttle 7, optic kill 8, choke 9 ...see where I am going?
Now you don't need a choke servo..so lets say you add flaps or gear....
All you need now is 4....but who knows down the road.....
Good luck and have fun