After months of flying a 3 channel park flyer, I'd like to start off with a radio and an airframe that can do aerobatics.
You'll still need to go with a trainer type plane to begin with, but you'll probably want something more like an Avistar than an LT-40.
....how many channels do you need to do 3D?
3! Yup, I've seen someone hover a Lazy Bee! But that's probably not what you wanted to know.....
Really 4 channel would be the minumum as many basic 3D planes only use the 4 basic functions anyway. They do usually use two aileron servos though, so you'll need a Y lead for that. The better radios will give you the option of ATV, expo and mixing, all of which will be handy for any aerobatic or 3D plane. Many of the computer 6 or 7 channel radios will give you enough options to play with for a while....