Don,
I hate acrylics, so take everything below with that in mind.
For me, by far, the best acrylics for airbrushing are the Tamiya acrylics. Also, for your applications, they have a wide range of colors suitable for autos, so all your cars don't look like WWII german tanks. Use the tamiya thinner. Some people use other thinner, but I am a big believer in using the thinner formulated for the specific paint brand.
Why do I hate acrylics? Because I've never found any, including Tamiya, that spray quite as nice as an enamel.