Hi, welcome !
If your going to use stencils - which is fair enough, try using a light grey to shoot through them.
bure black, and pure white are rarly used in airbrushing. theyre some times just TOO strong.
When beginning, think in 5 levels.
level 1:White
level 2:Light Grey
level 3:Medium grey
level 4

ark Grey
level 5:Black
try mixxing a small amount of each, ready to spray, use
#2 ( light grey) to rough out your work, or blow through your stencils. then start adding areas of shading with this colour, it will act as a kind of underpainting.
the bulk of your detail will eb done with the medium grey ( #3 ) and so on.
the beauty of these 3 shades is that its not over complicated. but by sticking to number 2. 3, and4 you ALWAYS have the possibility of making certain things alot lighter ( extreme highlights / reflections) and darker ( extreme shadows ) with #1 and #2
Try it out
Rick B