I've never really seen the point of having a stock unless you're using a remote line (Tank on your back attatched via a cord), whenever I've tried one I think they just get in the way, but each to their own
As for barrels, I really don't think you can beat a Custom Products barrel or a Un1tec barrel, J&J ceramic barrels are pretty good too, but the best barrel I've used on a Tippmann is probably a custom products 14" 1 piece barrel, LiPS sell them I think, nice and accurate.
The Ceramic J&J barrel boasts you can shoot through breaks, but to be honest I think it's a load of crap and they're not as accurate as the CP one from my experience, cheap though.
Un1tec barrels are freaking great, I have one on my G3 and SLG UL and love them, but I'm thinking of swapping them for a CP barrel after seeing how great they are on a Tippmann
Er, yeah, to summarise, I have a J&J Ceramic and a CP 14" single piece barrel for my 98cp that I use on public days with friends and I prefer the CP barrel. I wouldn't bother spending stupid amounts of money on a barrel kit that costs more than the marker you using though, save that for when/if you upgrade