Glad to hear you liked it! The biggest part of joining a team is looking for one. Try the tournament section of the forum and look/ask for teams that need more people: Some of my best games were just adding onto a team that was a player short. Teams naturally are more organized and willing to act as one on the field, which is excellent for paintball.
There are two sides to training: Personal and group. It's very important to stay stretched out to avoid sprains and pulled muscles. Even if you just start by doing it before a game day, start stretching out and doing light cardio work like jogging to keep your body used to moving around. Group training doesn't have to be done with a team (though it helps). Start by taking a bit of a leadership role on the field: Get your side together really quick before the game starts and figure out a simple plan. Even the simplest "go up the right side" is infinitely better if the whole team sticks to it and watches each others' backs. The more you play, the more you'll figure out what plans work, and what doesn't.
As far as paying goes, if you're talking about paying to play normally, then everything is the same, only cheaper. I don't have any experience with Delta Force, but generally you can expect to pay a lot less now that you have your own kit. Playing on a team you pay for everything just like you normally do. Very rarely will an amateur team actually have a sponsor who pays for things: Paintball just isn't that big, yet!
If you do get on a team, you might ask the owner of the field if you can get a discount on your paint, since your team will be buying more of it at once. Don't push them for a bunch of hand-outs, but asking 5 or 10 pounds less on a box of paint is reasonable.
