Usually, you balance a model at the fuselage. On your biplane, since it says to balance on the upper wing, just project the fuselage sides up to where the projection intersects the bottom of the upper wings. Balance there.

Don't balance at the tips because any dihedral will add an error and make the model look more balanced that it may actually be.

As far as the ailerons are concerned, where do the instructions have you mount the servo and pushrods? That would be the first determining factor. Where are the horn mounts located? Where is the servo or servos to be mounted? And so on. An ARF kit should give you some guidance about control system installation.