What Agent Arizona said. It's extremely cool, but not worth it. As far as airsoft goes, I've played airsoft with my cousin around my house a few times in Mando helmets, and because the helmets were plastic and the BB's are small and plastic, they don't do any damage. However, any costuming helmet is going to be extremely hot, provide poor visibility (for the most part) and probably break. Airsoft around the house in cheap plastic helmets you don't care about is one thing. Playing an actual game with fiberglass/bondo armor that you spent so much time working on is totally not worth it. The helmets we used were just the Hasbro Boba helmets you get from the store. I would never use my actual helmet for paintball and probably not airsoft. Before playing, we made sure that the helmets could stand up to AEG fire at 5 feet away. It was probably dumb of us, so I wouldn't even recommend this.
Also, there's a huge difference between a plastic BB and a paintball. Sure, paintballs tend to shoot slower, but even with a lower velocity, paintballs have a lot more mass and, if you've been shot by one (which I'm assuming you have), you know they hurt a LOT more than plastic BB's.
In short, costuming armor is not meant for playing like this in. Looks cool, but it's not practical or safe. Just don't do it, please. K?