Welcome to the world of less fumes, easier clean-up and Windex!
Thinning is dependent on many factors. The rule of thumb I use is the consistancy of 2% milk. I use Tamiya Acyrlics with their thinner and just eyeball the mixture, but if I were to put a number on it it would probably be 60% paint to 40% thinner. A caution when thinning acrylics with isopropyl is tip dry as the alcohol can dry so fast it clogs up your airbrush. Needle lube such as Badger's Regdab or the Iwata-Media Super Lube helps prevent that, and keeps the needle moving freely to boot! You may want to investigate using an acrylic retarder (found at places like Michael's) to slow down the drying time.
Using a primer is a matter of choice. Acrylics need time to cure and are often still "wet" even though they are dry to the touch. Before they are fully cured they are quite susceptable to lifting, especially if you use tape for masking with. Once they are cured you shouldn't have any problems. However there is no guarantees in life! I rarely use primers, but when I do I throw marital bliss to the wind and use Tamiya's AS-12 Aircraft rattle can for (duh) aircraft and their Primer for everything else. I've heard of good results with Krylon as well, but keep forgetting to buy some...
I also suggest giving the styrene a wipe with the isopropyl before painting to remove any residual detergent and oils from your hands.
Washing up acrylics is simple, I use Windex with ammonia. Windex will also remove acrylic paint in case of a booboo.
One caveat, though. Even though acrylics aren't as smelly as enamels, they still smell. My wife if hypersensitive to odors and complained about the fumes until I bought a jar of enamel home and opened it. She has since realized that I'm going to need to paint with something and accepts the acrylics as the lesser of the evils. Good luck!