You can install it anywhere. However, be aware that it is plated spring steel, not stainless. So, it will probably rust fairly quickly in the outdoor environment.
This particular door stop is 4 inches. There are longer door stops available in different styles, like model 14505, Satin Nickel Step-Release Kick Down Door Stop.
Yes, I suppose you can I never thought of that because we have always installed door stops on baseboard. It might work better if installed on door
The silver plate opposite the bumper unwinds from the spring. This plate is mounted to the wall or baseboard w the included screw through the center pre-punched hole. There is a small hole/notch at the perimeter that the end of the stops spring winds into. You keep feeding more of the spring into the notch turning it clockwise until it secures firmly. Easy Peezy.