Different brands of servos are said by some to rotate in different directions. Anybody know the differences for sure?

If you're using the same brand throughout, the usual practice is to have the two aileron servo arms both point out or both point in, and to have the servo arms on the two flap servos both point either right or point left.

Changing one of the flap servo arms to point the other way should only be as hard as moving the location of the flap horn on one flap. And pulling the servo arm off and putting it back 180degrees.