Hi Leonardo,

One aileron servo is certainly enough.
I did this using standard strip-aileron torque rods and one central standard servo.
I agree there is no need to dig into the foam for two servos.

Also, if you keep the weight down (check my thread for numbers) you will find that with low rates and some expo on aileron and elevator, this model's low speed performance is like a standard low-wing trainer. It lands very slowly and not once did I get an unintentional snap.
I suspect that those that have experienced this, had this happen due to excessive wing loading, aft CG, and maybe also extreme aileron movements. I find the model is easier to land than a low-wing trainer.

The wood cowl is good. Fuel proof it well and you will have no problems. I think it absorbs engine noise better than a plastic or f/g cowl.
The .55 engine will be very suitable.