yay on the airbrush. but keep in mind you're going to have to buy a compressor there are small ones you can usually find in hobby shops for airbrushing, but i would recommend going ahead and getting a full size shop compressor from Sears or something, you'll get better delivery. I got a smaller one and when it's running it's only at 20psi or so when optimum performance would be closer around 35 to 40psi.
Respirator! This is the most important, even more so than the airbrush. there are air filters can get from 3M from Lowe's/Home Depot that work okay, and there's also clean air supply masks. Depending on what kind of environment your working with, clean air supply is good for indoors whereas a regular filter mask should be sufficient if you're not in an enclosed area, just make sure the filters are adapted for your particular painting applications, some paints (like those used in painting cars) contain harmful chemicals that will go straight through a filter mask and even absorb through your mucous membranes and skin, so for that particular situation you would need a clean-air supply and a chem-proof coveralls.
I bought an Iwata Eclipse HP series brush. It's a pretty good brush, not top of the line, but also not bottom of the barrel.
colors (can use your own paints, but i would recommend starting off with premade colors specifically for airbrushing applications.
-Etac and Aquaflow are decent water based paints though i've been told uro-based paints are better, check out SEM and House of Kolor paints.
You'll probably want to buy some extra needles just in case you tap the one in the brush and it gets bent.
While the airbrush is on one hand a very intuitive means of working, it has some nuances such as overspray that make it very difficult to master, but the speed with which you can lay down even colors i find gratifying enough, and the softness you can achieve is great. I wouldn't necessarily say airbrushing is more difficult than other mediums, i find it easier for me than watercolors for instance, it's just a matter of familiarizing yourself with the required techniques, but as i said before, the speed with which you can go back over an area makes it pretty forgiving in some instances, so don't let the difficulty dissuade you, hasn't been one area of art where i could just pick up my tools and think "Wow, this is a cinch!"
As for maintenance, if you keep the inside of your brush clean, it'll run fine with little other maintenance. I like mine sparkly clean so i usually take the extra five minutes to clean the outside but it's not really necessary.
You just have to inspect your equipment regularly enough to ensure you don't have leaks in your hoses (and face masks or moisture buildup in your compressor. Also be sure to check the inside of your mask periodically to ensure that there isn't mold growing in there or you might find yourself in the hospital with mold poisoning via inhalation. ew...
So there are alot of things that are required before you can even start airbrushing many of them rather costly, but you get out of it what you put in. So i say yay on the airbrush.
"Today, a young man on acid, realised that all matter is merely energy condensed to a slow vibration. That we are all one consciousness experiencing itself subjectively, there is no such thing as death, life is only a dream, and we are the imagination of ourselves... here's Tom with the weather." - Bill Hicks