Patrick,
Well, you got the r/c bug that has hit us all. If you feel that this is a hobby you will want to continue in then buy the best radio you can afford (maybe one step higher than you can afford). You can fly a single channel airplane on a 9 channel radio. Extra channels
just mean you can drive that many serperate functions at once, dont have to use them all on every plane but it is nice to have the option too. Most people will need a minimum of five channels once they have progressed past trainers (ie: retracts, flaps) and some will require more depending on type of aircraft. Get as much radio as you can afford so you wont have to purchase anouther system down the road, it works out cheaper in the long run.
Welcome to the world of R/C, now the addiction starts
Todd