The perfect starter gun: A Tippman Model 98. It's a decent gun out of the box, and it's very easy to get upgrades for it. Almost all the people in my dojang use Tippman Model 98s, with an added expansion chamber to increase distance. You could also get a flatline barrell. This puts a back-spin on the ball, increasing accuracy.
In addition to the gun, you'll want to get an additional tank or 2. I'd reccomend getting some 20 oz tanks, or, if you can find one, a 32 oz. The 32 oz ones are hard to find, but if you can get it, it lasts for a long time.
There are a variety of masks you can get. There are a few things you want to make sure of when purchasing a mask:
1. Does it protect the temples?
2. Does it protect the ear?
3. Does it wrap completely around the head?
4. Is it fog resistant? (This IS important, they have a tendency to fog up in hot and cold weather)
Also, it's smart to get a good set of shooting gloves. Getting hit in the fingers hurts like all get out.
Finally, and this is very important if you're a guy... WEAR A CUP!!! The last thing a guy needs is to get hit in the gonzagas by a projectile going 300 feet a second (especially if you're opponent has automatic fire!!)