A: Yes it can be used for that on a threaded compressor coupler
A: Definitely yes. It is nice and thick and soft and pliable.
A: Yes, this can be used for threaded connections for compressed air.
A: Yellow Gas Line Thread Seal Tape with PTFE is recommended for LP connections. It is thicker than Fastape.
A: If it doesn’t say on the package as use for gas then it’s not for use on gas
A: Yes, and No.... Yes it will work, and no it is not the correct tool for the job. PTFE is impervious to gasoline, but the problem comes from the type of application it might be used on in a gasoline environment. Tapered threads can be easily over tightened with PTFE on them but the worse problem is from little pieces of PTFE being introduced into a fuel line and carb/injector system if the tape is not perfectly applied. Rectorseal #5 is probably a better choice as long as you don't over apply it. Also there are Locktite products made for gasoline line applications on threads.