I've run 3 simple pneumatic props the last few years that all used a single, 12" dual-action cylinder each. And my compressor is practically running non-stop.
This will of course depend on the traffic you have, but we would hit periods of time where there would be a constant flow of people coming through. We queue them up into small groups, but even at that rate I could hear the compressor out back buzzing away.
Right now I have a Husky branded compressor, which is essentially this unit:
http://www.harborfreight.com/8-gal-2-hp-125-psi-oil-lube-air-compressor-68740.html
If I had to do it all over, I would've got this unit:
http://www.harborfreight.com/21-gal-25-hp-125-psi-cast-iron-vertical-air-compressor-61454.html
I have a single line running from the compressor into a manifold that splits the air lines out to the individual props.
The idea of using reserve tanks may help you get through peak periods, but a small compressor is still going to have to peddle to catch up and replenish those tanks as well. Lately I've been worried about what if my compressor were to die, that's pretty much the end of those props, so I've been thinking of adding some redundancy to cover the need for more air and as a backup.