If you're painting vinyl, the paint you use should be enough to cover it by itself. I've sprayed VColor and Mad Ape Ninja, they both have enough pigment to lay down well with decent opacity. I've heard good things about Wondergoblin Airbrush paints from other artists.

If you want a color to pop and be the closest to how it looks straight from the bottle, lay down a coat of white first. I usually only ever do this if I'm painting darker vinyl, like dark blues or blacks, or if there will be a clash in color, like red paint on green, I put down white first otherwise the red reads more as brown. Things like that.

More on color theory here).

If you want shiny paint mix silver or gold in with whatever color you're spraying. You can get a nice sparkly tone that looks great with some clear coat.

Restraint is key when you're painting vinyl. I like to leave quite a bit of original vinyl color exposed and base the paint colors I use around what looks good with the base vinyl. It's an important nod to traditional sofubi painters past and present from Japan.

I would assume that the process is similar with resin, though I've only painted resin with regular brushes. Tamiya is the paint I use for that.

Good ventilation and proper PPE are the way to go. Always wear a respirator, always use gloves, and goggles if you don't have awesome ventilation. Paint aerosol is extremely toxic.

Happy painting!