Compressor HP question.

I doubt it. Such compressors can go up all the way to 100-150 psi, while you would only need no more than 30 psi.

I don't think we're talking about the same thing.  The Paashe D500SR I looked at  only goes up to 40psi.

My Porter Cable goes up to 150 but that is for woodworking with a 6 gallon tank, and a different beast than the Paashe and very loud.

Horsepower vs pressure depends on flow rate.  The more flow at any pressure, the more horsepower required.  Most airbrushes have a pretty low max flow rate, so airbrush compressors do not need a lot of power.

Further, one way to reduce power needed is to reduce leakage.  Wrapping threaded connections with teflon thread aided the pressure I can achieve with my pretty wimpy Iwata compressor.