The fundamental principle of question one is that mass doesn’t change the force exerted on something. For every action, there is an equal and opposite reaction. So when the bug flew into the windshield, it was exerting an equal force to that of the bus, but because it’s mass was much smaller, it couldn’t withstand the acceleration of the interaction. Because of this, the bug didn’t survive.
The fundamental principle of question number two is that rockets can accelerate. An object doesn’t need air to be the “equal and opposite reaction” of an interaction– it could be something equal and opposite created by the object itself.
The fundamental principle of question number three is to understand that just because force may be equal in an action-reaction pair, acceleration doesn’t have to be the same. A bullet will accelerate much quicker than a gun because the mass is much smaller (acceleration and mass vary indirectly).
The fundamental principle of question four is to understand that inanimate objects can exert forces too. Also, it’s to understand that if the tension in a rope is the same in two different circumstances, the amount of force the objects are exerting on each other in both situations, is the same.
Identifying action-reaction pairs is quite simple. The first step is to identify which two objects are exerting equal and opposite forces in a given interaction. It’s not always an object you would immediately think of (i.e. the ground pushing the elephant up and the elephant pushing the ground down). Also, usually the equal and opposite reaction occurs between the two objects that are directly connected to one another (i.e. the baseball going into the glove is exerting an equal and opposite force to the glove, not to the arm pushing the glove).