Not familiar with the kit, but from the skeletal wing image there is a single aileron servo. If you want flaps they'll have to be just the inner variety and will require two servos (one for each side), as you mentioned using micro servos, unless you figure out some kind of torque rod arrangenent to drop the simultaneously from a central servo behind the aileron servo. If using a "Y" connector from a single channel remember to offset them so you don't have beautifullt symetrical servos with one flap coming up and the other going down (a common error). And the only way to fix it once it's built in and covered is to flip the servo arm and then make one control rod longer than the other and forever after you'll bank slightly when the flaps come down.
And don't fall into the trap of thinking R/C has any similarities to full-scale. You don't use your feet in R/C and you NEVER fly at yourself in full scale (when intuition is backwards). The theories are the same but the application is not. (I got through ground school and 15 hours in CAP and college Avaition Club).
I would not bother with a retractable tail wheel with doors on a 65" model. They gave them up as too heavy and problematic for the minimal returns on the full scale Spitfire. You do not need added weight in the tail of a P-51 unless you want it to fly like a Brewster Buffalo ("stodgy").
If you try to do too much . . . . You'll never get it finished
Sage words.
Take a look at what I've wasted months on for a ARF with no retracts and only the routine four control groups. Redundant battery & switching for the receiver, electronic ignition for the (gasoline & sparkplug) engine, isolated kill switch with fiber-optic actuator (so it won't have inductive interference to the receiver through the the component wiring). Madness.