RE: Multiple servos for elevator?
Here's several of the possible arrangements.
The first is the common one, as both servos are usually back-to-back in the rear fuselage. The arm pointing up has less up movement at the elevator, as it moves down on its motion around the servo output axis, while the down pointing arm moves up. The difference is small but it is there.
This also occurs with the second arrangement.
The servo can be reversed at the transmitter, requiring 2 channels and mixing, or one can be internally reversed, and a y-harness used on a single channel, no mixing needed.