The Javiln that it comes with is pretty sweet. LAPCO's are very sweet with Low Pressure Setups, very efficient. A bit on the loud side. I've heard nothing but good things about the total freak and plan to pick one up when I have the cash. Boomsticks are also very nice barrels. Or if you could pick up a CP barrel set (JT, Avalanche, Warped Sportz, etc) Those are also very nice. It's pretty up in the air, what ever you want depending on how much you want to spend.
I'd get the .684 Javlin, the LAPCO autosprit (.686) and the LAPCO Big Shot (.689) that should cover you pretty well, and it wont set you back more then $100 or so.
As for air systems, can't go wrong with Max Flow. I've heard that the newer Angel AIR's have the bugs worked out. Centerflag also makes good air systems. Again it's up to you and how much you want to spend. But as the Excaliber is very low pressure, go for a 4500 psi system, unless you're a front guy, I'd go for an 88/4500 system, it will give you a great number of shots even when you can't get a true 4500 psi fill.
-Micah