4oz is more than enough for at least 2 pistols.
That is assuming you use an airbrush and not a HVLP sprayer which would result in alot more overspray.
madd0c
Lauer Custom Weaponry (the manufacturer) sells a complete kit with a cheap airbrush, propellant can, the duracoat, duracoat reducer and tru-strip for $49.95
It is what I used to finish an m1a stock as my first time ever using duracoat. Worked great, though if you have an air compressor I would hook the airbrush to it and not use the propellant can. You won;t be worried about running out of propellant. The airbrush in the kit comes with the adapter for a compressor.
I highly recommend the kit as a starting point, mine turned out fine (at least I think so)