last question first a 60 size plane is one that requires a 60 size 2st as the minimum for flight.
your going to want a larger engine than that for the spit if it ends up being 8lbs or more.
the sizes I listed in the previuos posts will be about right something in the 75 2st range would fly the plane for you even better would be a 4st as they swing larger props as well as have a nice sound for a warbird.

for servo placement the spitfire is a tail heavy plane so mount the rudder,elevator,and throttle servos, as close to the center of gravity as poss, not in the tail or your going to be adding alot of weight in the nose for ballance my spit has 19oz of lead in the nose for ballance and the servos are located in the center of the fuse.
the wing on the other hand is another story yes it is a good idea to make servo hatches for the ailerons,its a much more reliable system for control and will reduce the slop that can occure with the control horn setup for ailerons.
with flaps the control horn system with one servo is fine because they don't get as much use as the ailerons.
cut a slot for the control horn in the hatch and mount the servo to the hatch using small hardwood blocks epoxying them to the ply.
your going to have to make some mounting rails so the hatch is secure to the wing.
typical hatch size is aprox 2.5"X3" for my 60 size planes I use a standard futaba 3004 servo.
when you open up the wing to make the hatch hole, start small and carfully enlarge it to fit your ply square/rectangle .
here is a couple of photos from my Top Flight P-47 wing construction for a typical example of servo hatches in the wing, the P-47 has individual servos for ailerons as well as flaps thats why there's 4 hatches,take notice of the shot of the wing in the Bones the hardwood rails are for the hatches to screw too.
your going to have to do some fitting but it's not that hard.