Get some cheap filters that you can risk losing just in case a wild BB goes in your direction.
As for games there are regional and city "clubs" and then teams within those clubs. Some have different goals (eg. PMC simulation, just having fun on a Friday night, sort of serious, Military simulation with ranks and "training" and all etc.) but you don't really need to join a "team" just be a part of the club.
When getting hit we play on honour system, if you're found to be cheating or purposely not calling hits you will not be welcome to future games. It's fine to not call once in a while but err on the safe side and call yourself out.
Actually I was thinking about it after one game and I realized I wasn't calling some of my hits that day in some of the firefights I was in. I didn't feel anything or hear anything hitting my gear but I saw them coming and did the "matrix" thing (they were firing .28's at me so going fairly "slow"). I'm sure at least one hit me but I didn't call myself out because I didn't hear/feel anything. That's fine, I'll know better next time but knowingly getting hit and shrugging them (rubbing your leg when your leg got hit) is a whole different story and if you do that you'll be asked to leave and never come back again.
As for ammo limits there are milsim games which are usually restricted to "real-cap" or low cap (comparable capacity to real steel counterpart eg. P90 = 50 rounds, M4 = 30 rounds etc...). Sometimes they will allow you to run mid caps with a limit to how many you can carry, eg. 3 x mid-caps of 68 rounds and unlimited low caps. As for regular skirmishes anything goes really. Hi-caps are generally frowned upon though, they "rattle" (because it's a "BB well" that uses a wheel to feed BB's), have unrealistic capacities (eg 400 rounds in a M4 hi-cap) and you have to wind them every certain number of shots. A better investment might be getting some mid caps and low caps, usually guns will come with 1 hi-cap and that's fine, really if you're using more than 1 hi-cap in a short 30 min skirmish then there's something wrong and you should go play paintball
.
Spectators are always welcome, especially if you have a camera. Bring a PB mask or sealed ballistics to the field (depending on rules governing eye protection) and a safety vest.
As for getting a ride. There's usually a "carpool" section where you can bum rides off other people in return for some gas money.