Is it okay to spray my dog?

It would be okay to spray him. I don't know if this aversive would work on your dog and his problems. For some dogs it could make the problem worse as they could associate the person at the dog as being someone evil. Then there are dogs that enjoy being sprayed with water. It would be even better to properly train him door behavior. This means to sit politely when the door bell in rung or when someone knocks. This can be done step by step. Start with just a basic sit stay and start adding distractions. If you don't know how to teach this, enroll in a good dog training class.