On my 90 or 120 size planes, I've used the std. servos without failure for the ailerons. For the rudder and elevators, I use the metal gear servos.

If you can locate the wing spar, that should be a close starting point. It's usually about 30% of cord location.

On the Spitfire, make sure with gear down, that the axle centerline is out at least to the wing leading edge. Otherwise you'll be replacing a lot of props from nosing over. Also, I'd suggest that you reflex both ailerons up about 3mm to create washout to slow tip stall till you get used to the plane. Most warplanes as you know will snap quickly if you rotate too fast or get too slow on approach.