These fittings are designed to be used for air and have not been tested for gas. So we don't recommend using these items for gas
Yes, it will work just fine. It is all brass.
All the threads are normal "righty-tighty/lefty-loosey" threads.
I'm running them at 90-110 PSI
One per package.
When I bought them three days ago, they were on a display board adjacent to all of the pneumatic tools in the tool section.