1) Open hole, a flap with a wing nut holding it closed, a flap on a slider. Many ways.
2) Drive full speed forwards and turn the transmitter off. Does it reset to 0?, does the weapons produce the same result?
3) Youll need a seperate PRV, rated to 1000 psi for full pressure or below your lowest components.
4) Yes, provided theres no one way section between components.
5) Same as 1, just get a ball valve of some sort or similar.
6) Unless an EO says - No, the On/Off needs to be directly after the bottle via either the paintball pin valve or via the bottle itself.