Here's how to do four aileron servos. If you're not flying a biplane, just have two right and two left servos....

http://www.futaba-rc.com/faq/faq-10c-2_4ghz-q682.html

Channels 9 and 10 won't be mixed...they are only on/off channels, or end-to-end channels.

If you go into the Aux channel section of the menus, you can set channel 5 to null and no switch/knob/slider will activate it. You can do that with any of channels 5-10.