Depends on your budget. Some people allot themselves 100 paint balls, and leave the field whent they run dry, and start the next round with 100 more. Other people carry up to 500+ paintballs (some in the hopper and a few hundred in containers on their belt), a squeegie, and even an extra CO2 canister so that they can keep playing no matter what crisis arrives.
You‘ll find that paintballs can go REALLY fast during your first day playing. Most peolpe have a tendancy to shoot at trees or walls or other equally wasteful targets, just because its so satisfying to shoot something.
Plus your accuracy won‘t be all that great to begin with, so when you see an enemy you‘ll probably blaze off 10+ rounds trying to hit them. That and if it‘s your first time, you‘ll probably be using the rental markers, which will not be as good as the ones the "gun owners" bring.
So you find your first shot each time will be more of a rough estimate to try and figure out the angle you should point your gun up in the air to "lob" a paintball at the target. Call the field ahead of time and find out if their rental have velocity knobs or screws. If they have knobs you can adjust you velocity with your fingers, if its a screw, then bring a set of allen keys, but don‘t let them catch you adjusting the screw.
Paintballs typically go for $10 per hundred when you buy them at the field. Don‘t go into your first time thinking that you will be able to play for a long time with 200 paintballs if youre picky about what you shoot at. Thats the most common mistake made by people trying it for the first time. I‘ve seen countless people with the saddest look on their face when they realise that they didn‘t bring enough money to keep playing.
I‘d figure on buying 500 paintballs, if your group intends to stay for a few hours. Don‘t buy way more than your friends right off the bat though, or you will be standing there with 200 extra paintballs or something, when they‘re all ready to leave.
I played from 12:00-4:30 on an outdoor field my first time, and I went through 800 paintballs.
Most games do have some form of time limit, otherwise you‘d have to wait forever for the last couple of people if they are camping. Sometimes theres no limit, but the ref calls the game when the action stops. Sometimes the games are based on objectives, like capture the flag, so that helps to eliminate excessive camping.
You‘ll see that they will run different types of games to keep it interesting. What you probably imagine paintball to be, would be whats called full field elimination, where both teams just go at each other using the whole field, with no objective but to shoot the other team.
Depending on the space (indoor/outdoor) you will see that you‘ll probably only play that once, maybe twice in the day. The rest of the time you‘ll be playing other games, where one team or the other has the advantage somehow and then switching it over the next. Like, one team will defend a makeshift town in the forest, and the other team must attack the town. Even though the attcking team knows exactly where the enemy team is, they are usually disavantaged since the defenders will be shooting through cracks and holes in the walls.
You‘ll be amazed at how accurate some people can be. I know that I can hit a space that‘s equal to are maybe slightly larger than the paintball from range within 30 feet, not always with the first shot, but within 3 for sure. If you think you are covered, but you hear paintballs hitting the wall, then probably you have something sticking out somewhere and you should make yourself as small as possible and do a check on the door to make sure they‘re not going to come in the room with you.
Anyway, you‘ll figure it out. You really should give it a try, it‘s really fun, and it‘s even better with a group of your friends.
If you organise a group to go and play, then most fields will give the "organiser" a deal of some sort. Like paint for $7.50 instead of $10 per bag, or a free gun rental ($15-$20) usually. Make sure you call ahead to book a time, and make sure to ask about deals.