I have the same set up as you are going to have.

Channel 1and 6 to the ailerons -- flaperon mixing built in
channel 2 and 8 to the elevators --- ailevator-9C has mixing built in so it is very easy to do
channel 3 throttle
channel 4 rudder
channel 7 or 9 battery

It works out nice because you can set trims and end points independently on both 2 and 8 to match servos.

The only thing I don't like about my elevators on channels 2 & 8 is that my back up radio is only a 6as so I can not use it in a pinch.