"what gun should I buy?". I would highly suggest purchasing a semi-auto. They are just a lot easier to play with to start. You pull the trigger and a ball comes out the end. Very nice.
DO NOT purchase a tournament level gun right out of the blocks. Most newbies that do end up spending more time working on it than playing (because they don't know how to care for it and they break it or get it so gooped up that it doesn't work right).
Practice, practice, practice. Practice shooting, practice loading and practice cleaning. When you get on the field, you don't want to have to think about these things.