Orlando, the idea is great, just like Lasershots but DIY.
Let's break by parts:
1) the gun, that part isn't complicated as you have plenty space and a rigid body.
2) the sensors, see if you can find lasershots pictures, they use a semi-rigid vest(no helmet, it complicates matters a lot) that has two lights on each shoulder and he battery pack on the back, sensors in the back, the chest and above shoulders.
in Lasershots, gun also has a sensor and a HAND sensor(IR bounce) below the front barrel guard that forces you to hold the gun in both hands or it doesn't fire(to prevent smartasss players from using their off hand to cover sensors) and connects with a cable to the vest back.
The "fire" is done with a visible red laser, but that's only for aesthetics purposes, below the laser there's a IR LED/laser and THAT is the real "bullet"(in which you can also encode the vest ID for stats tracking if you wish)
Of course you can make the gun independent, but that adds another battery to manage... more weight... another couple wireless modules, more cost, etc
If you can go that way with the design it simplifies things.
For wireless, simplest is Xbee, next you have bluetooth that has long range but is more expensive, there are lots of really small modules and some shields for xbee and BT(there's an Arduino Bt as well)
Expanding the idea a little, you could have a central command to monitor ALL players(since you use RF, you can remotely enable/disable all vests at game start/end, collect statistics to be printed out for players -players love those things-, even "awards" for special feats at an extra price -more income for you, more engagement for the players-)
the sky is the limit, and the power consumption as well!