With the 9C you can also purchase a synthesized module that will allow you to switch to any channel without changing xtals. That way you can fly all of your aircraft with the same transmitter even if they are not on the same channel. Just a turn of the screwdriver and you are ready to go. As said above, the 9C will transmit in either PCM or PPM (FM) modes. It will work with all of the receivers that you have now and if you decide to upgrade to PCM (which I recommend) in the future you just need to replace the receivers.

The 7C will be enough to fly with but you will want more capability as your skill level progresses and the 9C will allow you to do that without spending more money. The 7C is also usable with only 1 channel. It is a matter or pay now or pay later and I recommend that you spend a little more for the 9C now and not need to spend more later.