Definitely this. Pull-ups themselves are a great warm up in my opinion. However, shadow boxing sounds like an excellent warm up for your tendons and ligaments in the arm/forearm and shoulders.
Seated Front BB Press to start, or standing if you feel competent, Military Press, etc. You could also try some handstand push-ups, which are brutal but ****ing efficient if you do them right.
First, what the hell is too much? Preference takes over when determining your training regimen.
Second, it seems like you're just starting, so it could be too much for you. Personally, I think rest...
Definitely go with this one. Google is your friend.
My advice to you is to try out some "intuitive lifting". Or in other words feel out your reps and sets, and see what you feel like could bring you...