If it is a metal foil it will conduct heat away from the motor, although it would probably still be best to take it off. If you take it off you should pull more heat off but it won't make as big a difference as if it is paper or plastic you're removing.

I don't don't have any experience with that helicopter of motor. I did own a CX2 and the easy rule for setting the gap between motor pinions and main gear is a strip of paper fed into the gear, press the pinion into the main gear, tighten and then spin the gear to feed the paper out. Absent a more precise method it should suffice.