As for thinning, that is an easy
question -- use simple and inexpensive Isopropyl alcohol, 91 percent.  If
you don't have any, Walmart is usually the cheapest, but Target and all the
drug stores carry it.
I also suggest rinsing your airbrush, paint pot,
and nozzle with water, and then rinsing with Isopropyl alcohol.  These
steps remove any dust or other contaminants.