Some questions i have. (New to paintball)

I am new to paintball and just got a spyder victor to try out and see how much i like the sport. A few questions i have for experienced players are, After getting a 20oz Co2 tank filled, how long will it last? as in how long before i have to use it. Another question i have is how good of a gun is the victor? If you can answer any of there questions thank you very much.