as for which thinner to use, Acetone will evaporate faster thinner takes longer so they affect how fast or slow. Mix them if you want.
How much has more to do with the size nozzle your gun has. Thicker for larger and thinner for smaller till you get the pattern you're looking for.

I use up old hardener in Rustoleum whenever I shoot it. About a cap full per qt of paint, then I reduce.

Give me ambiguity
or give me something else