I use a Pasche airbrush for duracoat as well. I only mix enough paint for the current coat and any leftover gets dumped if I can't find something else to use it on. You only get about 20 minutes of open time before the paint starts setting up. I never purposely wait for a coat to dry before adding another layer but because I'm usually painting a lot of pieces the first one is always dry to the touch when I go over it again. I agree on not using the reducer, play around some to get a feel for the process.