What is the limit for the length of a paintball gun barrel?

I have a tippman 98 custum paintball marker. It has a response trigger, and i have many dif. barrels all dif. lengths. ( custum, 12, 14, 18 in barrels) I use the 18in. barrel, but it has been giving me some problems with range and accuracy. I havnt used the other barrels lately, but i might start using them to see if there is a dif. But is there a length i should not go over? and is a flatline a great idea for woodsball?

What’s the best type of paintball gun for an intermediate player looking to get more serious?

I’ve been playing for a couple years, but usually just rented equipment. Now that I’m in college, I’ll be able to go a little more often, since there are much closer fields to me now than there used to be. What’s a good all-around gun? I was thinking the Tippmann A-5, most likely the Stealth version. Any suggestions? Please, no unnecessary negative comments, unless it is pointing out the flaws of a paintball marker.