Hello, time for another introduction!
Now a couple of questions..
How will other (older, more experienced) people treat me on the field?
I think you'll find that the majority of airsoft players are only a bit older than you. In general, there tends to be a good turn out from the 14-18 year old crowd, so you'll have company. Some events are 16+, or 18+, so obviously you'll have to wait to get it on those.
If you comport yourself with honesty and maturity you'll be fine.
Honestly, black gear isn't really the best for most outdoor environments. Black isn't a "natural" color and tends to stand out. In airsoft, however, it's more important how you use terrain and cover than what your camouflage is. I played an event a year or so ago where I wore a bright blue jacket and had no issues sneaking around by just keeping the majority of my body behind cover. Camouflage is certainly useful, but at airsoft ranges, it's more important to make use of the surrounding terrain to avoid detection than to rely solely on your uniform.
There are as many game formats as there are different fields. Some games are recreational and tend to be quick, ten minute affairs. Others have objectives and might last for hours between official breaks.
Generally, airsoft games break down into three types:
Recreational - No story line or camouflage requirements. People are out playing to have a good time and a variety of different mini-games (capture the flag, defend the castle, rescue the downed pilot) might be tried over a period of several hours.
Scenario - The event will have objectives and camouflage requirements. Each team will be attacking or defending different objectives or trying to complete missions.
Milsim - Strict camouflage requirements, more complicated objectives. Teams are typically broken into squads and each squad is assigned a specific function. Radios tend to be a necessity.
The differences between what constitutes "Milsim" and "Scenario" get a little blurry, but in general milsim is a bit more "hardcore" than scenario.
Arrival at a game:
When I arrive at an event, the first thing I do is find the event host and register with them. This typically involves filling out a waiver and paying the entry fee. As soon as that is done, I head back to my car, load up a single magazine and plug my battery into my gun. I then head over to the chrono station, fire my gun over the chrono and get it tagged with the appropriate zip-tie.
Typically zip-ties are used to indicate what the gun's velocity and Minimum Engagement Distance (MED) is.
In general, you'll be good-to-go as long as your rifle fires at or below 400 FPS.
After I chrono, I'll head back to my car, load the rest of my magazines, check out my gear, test my radio, grab my goggles, etc. Once I'm more or less ready to play I'll typically break out a camp chair and relax until the event hosts gives their safety briefing and outlines the objectives for the event.
Honestly, if you're a new player I would wait to purchase a sidearm. Attend a few games first and then decide if you must have a sidearm. It may be better for you to take the money you were planning to invest in a sidearm and invest that same money into purchasing more magazines for your primary rifle.
Asking yourself: Would I rather have more magazines for my primary so I can stay effective in a fight longer or a pistol which I might only use rarely?
In conclusion:Honestly, the best thing you can do is head to out a game. Michigan airsofters are a pretty friendly bunch and veteran players tend to be more than happy to help out newer players, make sure that they're comfortable and playing safely. People at games are usually pretty approachable so it's not big deal to fall in with a group of guys who seem to know what they are doing. Hell, I've been playing since 2006 and that's basically what I still do.
The most important thing is to play safe (keep your goggles on! Treat your gun like a real firearm!) and have fun.