I still haven't even flown my plane but I feel I can give a little bit of advice, anyone feel free to correct me if I am wrong.

From what I have read you don't want a full 3D plane as your second plane, you will probably still have a lot to learn after you have retired out of your trainer and should purchase something that is capable of aerobatics but is still relatively easy to fly. Many people I have talked to also agree that trainer time does not translate into knowing how to fly, my 11 year old brother has played (and I use that term on purpose) FMS and Aerochopper quite a few times and he can handle the plane but I won't let him touch my LT-40 until we are both fully certified as able to fly by an instructor and I have seen him demonstrate ability to fly (I plan on gettin an electric soon I will let him play with). Make sure to get checked out by your instructor and maybe ask around the club and see if you can try some more advanced planes on a trainer box and see what you think you may be ready for. If you can fly 3D then by all means do so, but unless you are sure you are ready you might just end up buying a reall expensive shovel.

As per your radio question I wouldn't personally go with a 9C as from what I can tell it is made more for helicopters that require more channels, a plane requires 4 channels and you can add a few other things on such as smoke and bomb-drop modules but I think that 9 channel might be a little bit of overkill

Again, my advice isn't from experience but simply from what I have read so take it at face value.