A lot of people like to start with the 9oz tank, but I prefer the 12oz. You don't even need thermal lenses in your goggles, although, those are the best kind if you can afford them. You will want a harness, hopper, squegie, barrel plug (most likely included with the gun), those are the absolute necessities, but you might want some body armor, gloves, neck protector, jerseys, and the list could go on for pages. If you want to know about more stuff, talk to your local field or pro-shop.