i use my 80 gal for my air. just put a air regulator on the wall and one on your airbrush hose.
it's a bounch of trial and error stuff in my oppinion. personal choice. some people like to clear w/ 1.3 and others like it bigger????? what ever gives you a good product.
small needle size makes smaller fine line. and your air pressure needs to go down and you'll need to reduce the paint a little more.
House of Kolor suggests reduceing 1:1 and most use med reducer no matter the temp.
I use martin senior's cross fire paint and i always use slow reducer in my airbrush and reduce it between 2:1 and 1:1. depending on the color. i reduce black less 2:1 and white colors 1:1
you just have to play w/ it to see what works and doesn't. like i said, it's what works for you.
my airbrush works between 15-35 psi depending on the detail that i'm looking for. the finer the line, the closer the airbrush to the surface and the less the psi. i switch needles also. a .2 needle w/ 20ish psi for fine line and my .3 w/ 35psi for true fire and some shading.
i like to use my .5 paschee brush for small graphic basecoats. like putting on a harley emblem. then i take my .3 w/ my iwata and do all my artsy stuff on the harley emblem. I'd also use the .5 to spray small flake (silver) around the edge of the flame. i use it where not too much control is needed but and nice consistant fade looks good. i'll also use it to shoot kandi (KK W/ sg100) over some of my small art work.
i use my touch up gun W/ a 1.0 to shoot the base color of my flames or larger graphics. keeps everything atomized well and the edges down, and i use medish reducer for my basecoats. temp has a lot to do w/ this. i might use slow or even fast depending on the temp.
i use my 1.3 for basecoating and clearcoating.
i use my 1.4 for priming/ or 1/64th flake
i use my 1.8 for etching primer.
i don't know if all of this is correct or needed, but like i said earlier. it works for me till i'm more educated and morph my style yet again. always changing never mastering!
good luck!