Power setting is your throttle and RPM. You get that from the cockpit!
Well yes, and no on the overheat. Most of the fighters in the game are modeled with non-WEP being continuous power, on the order of it is a rating that can be maintained indefinitely, or in some cases (on some planes) a 30+ minute rating. Since no sortie in this game will probably last that long any way due to fuel burn, HTC does it this way. WEP is of course limited and had overheat limits (cutoffs).
Bombers, on the other hand, don't work this way... They never flew even max continuous. They cruised when climbing. WEP was truly only for catastrophic emergencies. They used max cruise at alt because of the ranges they flew, and they didn't take off with any less than full gas. Whatever the max fuel allowed by their bomb load, they took off with that. Even when bombers took short runs across the channel into France, they always took full fuel. They were bombers, they needed it. They were not performance monsters, they were not uncatchable, and overall they were more worried with getting the job done in a repeatable way than in getting it done so fast it destroyed the airframe and all the engines onboard.
That's the problem with level bombers. Even in the heat of combat over a target they were cruising. In the heat of combat fighters were using max power because of the totally different philosophies behind the bomber/fighter design.
So, yes it would probably be nice to have overheat on all of them but for the most part this doesn't affect fighters as we have them now, and WOULD greatly affect bombers. End result: If you just add it to bombers the problem is solved. If you add it to all, well the problem is still solved.