Welcome. This is possibly one of the nicest, succinct first posts from a newb I've seen so far this year. First, I'll get the obligatory "get age verified" disclaimer out of the way. See the following post:
Fill out your profile so others can suggest an AV'er in your area. (Note: this does not absolve you of actually contacting them yourself.)
1) For a CQB match, a pistol is sufficient. Don't be surprised, though, if you occasionally find you're up against CQB rifles. For a milsim, a pistol is insufficient - you will require a primary rifle or support weapon. Your pistol is your secondary.
2) Radio & hydration is mandatory. Flashlights & kill-lights for night play also. Emergency first-aid kit is optional but nice to have.
3) There are AEGs that have electric blowback - they suck for the most part. More moving parts increases the odds of something breaking in the gun.
4) M4 style rifle - lots of customization options available. Current choice for a first rifle is a Kings Arms M4 AEG.
5) Some paintball fields can be hired out for airsoft games, often hosted by established players. There are also a number of private fields that hosts games.
6) Comms are useful, even during skirmish games. They can help you determine hot spots, call for help, or execute maneuvers without giving your position away.
7) Depends on where you live. Outside of city limits, go nuts (away from public eyes). Inside city limits, most have non-discharge bylaws that prohibit shooting anything outdoors. In such a case, practice in your longest INDOOR space.
8) There are established teams, but most milsims also have a general sign-up - pick your side and the CO will organize the various individuals into units/elements. That is, being part of a team is NOT a requirement to attend a milsim.
Again, welcome. Have a pleasant stay.