Well as real pilot that flies this plane, once you have started the taxi, if you put idle, the speed of the plane continue building up, with the consecuence of the constant use of the brakes.
The primer its not used as you mentioned, you prime the engine, and after you prime 2-3 secs you stop, and start the engine, not necessary you have to have a successuful start, maybe you need to use the primer again.
The carburator heat, ATM doesnt works or at least the RPM are not affected.