Amy's given some awesome advice (wow, what a great start you have on those models, I think varnish appy is probably the hardest color next to some shades of grey), already.
Carol Williams publishes a book about Color Techniques (not sure of the exact title, but you can find out mroe about it on her website, www.riorondo.com ) that really gives you perfect formulas for mixing up the right coat color out of paint, either oil or acrylic.
I used to love to use oils, mostly because they DID take so long to dry, and I can never leave anything alone, I had lots of time to get the blending JUST right, but acrylics are good, too, and there are driers and retarders to help speed up the drying time, or "slow" it down, depending on what you want to do.
One thing I want to add is to read the labels of whatever it is you are using, such as primers (spray or otherwise), and heed the warnings, wear safety equipment and use these items accordingly.
Most acrylics are safe, but when you make them airborne as in an airbrush, you change things, and I don't think it's a good idea to inhale anything like that, even though it's supposedly "safe", use a respirator (those dust masks don't cut it!) and use anything "iffy" outside, in a well ventilated area, as well as using your respirator (this is what I tell my son, and I kick his butt if I see him doing otherwise!).
Sorry to be a bummer. Most of all, have fun!!! I wish one day to get back to painting and customizing. I have a few resins around here that need coats of paint.
Post pics when you get going!
Liz M.