Well I am an airbrush artist as well automotive painter and I can answer a few of your questions. I will divide them into two categories, models, and real.
Models:
1. I use HoK, PPG, and Dupont on real stuff. However I have seen people use HoK on models, as well as the DuPont Variprime. HoK colors have special reducers (similar to thinners, but the chemical make up is different, thins the paint while keeping cure time relatively slow, and so on). Depending on the paint/primer you will need a certain reducer usually (i.e. PPG Duracryl 426 paint needs to be reduced with PPG Duracryl 105 Reducer). If you are worried about the eating of plastic test it on some scrap.
2. I suggest trying out Future floor wax to clear coat if you are worried about the decals, I have heard that works.
3. Pinstripe brushes are much different than regular brushes. The pinstriping brushes have about 2-1/2" to 3" bristles with a short 3" handle. There are different types of brushes for different applications. The most commonly used brush is called a sword brush. For products check
www.eastwoodco.com
4. No idea...sorry.
Real:
When reducing paints make sure to use the correct reducer. Certain paints have certain reducers as I stated above. The worst thing to do is cross breed. That can result in horrible adhesion, as well as bad finishes.
Another tip about real painting, stick with the same type (i.e. acrylic-urethane base, use acrylic-urethane clear, or other acrylic-urethane layers.) as well as the same brand (i.e. HoK surfacer/primer with HoK base, and HoK clear) all the way through.
General tips:
Be careful what primers you shoot through an airbrush. Dont try to shoot high build primers (i.e. PPG K36 High Build, PPG K38 High Build) through an airbrush, and that also goes for epoxy primers. The general rule for that is to try to avoid using any two part (catalyst and base) primers, surfacers, or paints. They can clog up the airbrush, or if they arent cleaned properly they are impossible to get out.
Always test. Thats it, whenever your trying something new, test it on some scrap.
If you need anything else just let me know.