Indeed, an hour or more of juggling things to make it home may sound boring but it certainly is riveting, and so satisfying if you make it
I don't know how well the mechanical systems are modeled in the game so I don't know what can help and hinder.
I've never seen any measurable drag from opening the radiator flaps so I don't know if closing them reduces drag at all.
Do the lighting systems put any load on the engine?
If the engine is damaged I try to find the lowest throttle position that will hold a steady speed and altitude and trim the aircraft to hold that if possible, then watch the temp and pressure gauges. Reducing prop pitch _seems_ to help but I can't think of any way to tell for sure.