I generally recommend starting with no more than 6 channels for some very good reasons. First, you need to learn how to FLY. Some people pick it up quickly, and others may take a few years. Either way, once you've learned the basics, you will need to get in a lot of stick time before you start getting good.
Now some people may say that they PREFER to use two channels for ailerons and two for elevator, etc. but the fact of the matter is, you don't NEED them -And it can take years to advance to the point of needing advanced mixing options.
Now let's fast forward a year or two... or three or four. Now you're a good flier. Do you NEED more channels? Do you WANT more channels? If the answer is ''Yes'', then you can go out and buy a bigger radio - BUT - You have several things going for you:
1. THEN you will have the advantage of knowing what you want, and understanding advanced features better than you do now.
2. You can keep your 6-channel radio as a backup in case your new one needs repair (it's ALWAYS good to have a backup Tx!)
3. (This is one of the most overlooked) Just think of how many new features will be available in two or three years from now. So when the next super-duper feature comes out, you didn't get stuck buying last year's model!