Get a compressed air/ nitrogen system as soon as you can, as well as an in-line regulator. Getting velocity consistency is the first key to a tournament-ready marker, rate of fire comes in second.
Barrels:
Look into Smart Parts Freak systems, Dye Boomsticks, Titanium Longbows, or similar sets. The mainstream thinking is that matching barrel bore size to paint is the key to accuracy, efficiency, and velocity consistency. Longer barrels don't shoot farther, that is total crap and you are best advised of it now. Anything in the 12-14 range will be fine, although some like 16 inch barrels. It is a matter of comfort for the most part; some people push air bunkers aside with their longer barrels.