10.8 V is fine. The battery pack is rated at a nominal 9.6V. You can safely operate down to about 9.0-9.2V.

For your airplane, just consider it a two servo model. Left and right ailerons. Turn on flaperon function, turn on flap trim. Adjust the percentages to suit.

The big thing is that you have two servos per aileron. You must make absolutely sure that the servos/pushrods/control horn geometry of the servos on the same surface is correct or the servos will fight each other slightly, and rapidly wear out gears. That's what the Futaba MSA-10 Servo Synchronizer was designed for. It replaces the "Y" harness for each side so that the travel, movement, and centering of each servo on the same channel can be perfectly aligned.