It said the piston is OFTEN needed when you upgrade with a HURRICANE kit, which includes a 120m spring.
Regarding the motor, it is said it cannot turn over even a 100 well, but with stock it will work fine.
And the gears are needed when you upgrade to metal bushings because of the small difference inthe shaft and bushing size of a half millimeter.
Leave it stock! It will work fine stock for CQB. If you plan to leave it stock there is no reason to buy these parts, other than the wiring, that is a good idea.