May I ask Is it necessary to use Vallejo Airbrush Thinner to thin it down at all? (I watched aa tutorial video where the instructor drop it directly into the airbrush without thinning it) And how much compressor pressure is recommended? Thank you!

I thin mine with 3 drops of thinner for every 10 drops of primer. Haven't tried it without thinner. It just seemed to me a little thick to airbrush directly out of the bottle. I shoot at about 18-20 PSI.

I get the best results without thinner around 12-15 psi i use a badger 105 with a .5 needle but i have done it with a badger krome at same or a little higher psi with .21 needle.