I need some help with the reccomended setup on my radio.

I have a plane with 2 Aileron servos (1 each half)
1 throttle servo
2 Elevator servos (1 each half)
1 rudder
2 batteries for receiver
1 R138dp PCM receiver

Could you tell me the best way to setup this airplane

I think what i need to do is activate Flaperon mode and Select a mix Program mix 1 and turn mix on and master would be Elevator and the slave would be aux 1 or 2. (Does it matter witch slave i use aux 1 0r 2 ?) I think link would be off and trim on, the switch would be set to null. Set the percentages on the next page to 100%. I still want to have all functionality of trims and sub trims to match the surfaces up.

To set up the ailerons on two different channels, you only need to activate the flaperon mix. Just set the flap movement to zero if you don't want flaps.

For two elevator servos on different channels, use the Ailevator function. If you don't want the elevators to work with the ailerons, then set the aileron amount to zero on that mixer.

You don't need to use Pmixes to get this job done.

Just follow the manual for such a setup. It's not complex at all.