As an automotive painter by trade I can assure you that you can use automotive paints thru an airbrush.All 3 of the cars I showed in my thread were painted using these paints.As long as you get your airbrush cleaned up by the time the paints "potlife" is gone you'll be fine.That's usually around 4 hours depending on things like temp and humidity.It's true too that the metallic content can look large on a model.What looks fine and "in-scale" on a 1:1 car can look like metal flake on a scale model so you just have to choose your colors carefully.
The main thing that will probably stop the average modeler from going this route is the cost. Automotive colors,clears,reducers and activators can be extremely expensive. You might think "I only need an oz. or two" but most if not all places that mix these colors can only mix pints as the smallest quantity.That's the smallest their formulas will allow. The only reason that I'm able to do it is because I have ready access to an almost endless supply of colors and supplies.All I can suggest is get to know someone in the industry if this is the way that you want to go(unless you're rich of course...lol).
Good job on your painting hrmodeler.