1. 1.5 is about normal.
2. Yes, gas will slowly leak out over time. If you keep the magazine lubbed though it will go a long way in prolonging it's life.
3. No, that's a good way to kill your magazine. If it does that, you've overpressured it and you'll blow the seals. You shouldn't fill it more than 5 seconds worth of gas.
"Someone in a Prius tried to race me at a stop sign the other day. I couldn't believe it. I had him for the first 100 feet or so but I can only walk so fast."