Toshi - As was stated in a different thread, any plastic throw away surface is fine for practicing, also shiny printed cardboard works well. The large plastic 2 quart soda jugs make a handy surface for practice, the curved surfaces are much like painting a model fuselage. Paper is not so good, the paint is just absorbed and you don't get the effect that the paint would show on a surface that is non absorbent. I use shiny cardboard, cut into 3 or 4 inch squares, easy to keep several on hand in drawer, any spraying you will do in testing will be a minor amount, one square will last for plenty of testing surface.
Depending on what city you are in, there may be a place or two that service air equipment or sell air hoses, they might well have the adapter you need for the air hose, perhaps a Graingers. Let your fingers do the walking through the phone book, I'll be surprised if you can't find what you need locally. It's a good idea to take both the air hose and the compressor to the place, they can see first hand what you need.
Any hobby paint is OK for model painting, like Bick and others are relating, the very inexpensive craft acrylic paints work very well too. If you are using the square Testors bottles, I think you are getting gloss paint. Just my suggestion, but that, (I think,) would not work so well for a three color scheme on your PBM. First, blending the color borders is a good bit more difficult with gloss paint, and for starting out as an air brush painter, I feel you would find greater success with a flat or semi-gloss enamel, for that Testors is my favored paint.
For thinning that paint, I think a good starting point would be 25% thinner, 75% paint. You may well find you need more thinner than that, I usually find it so, but the test results will tell you when you have the right mix. I have often found that 50% thinner works well. Do not be discouraged if you find it a rather demanding process, learning to airbrush paint. It took me a LOT of practice and time to become comfortable with it, but the pure enjoyment and satisfaction of becoming proficient and confident will be a huge reward. Once you get your equipment working well, I'll bet within a week you'll be a very good painter.
I can imagine you are a careful and meticulous person, so cleaning and maintaining your airbrush will likely be something you will do well by nature. But just one caution, if you try acrylic paints, the immediate cleaning of the airbrush when finished painting is important. If the paint is allowed to dry in the airbrush, (and it doesn't take very long,) you will have a real chore to get it cleaned up later.
Relative to your question about places to visit for learning, one for certain that I seriously recommend is Don's air brush website, jut Google Don's Air Brush and you will find out pretty much what you need to know about the subject. I had been in the hobby for well over 45 years before I visited his site, then I learned a great deal more than I had known before. Very well worth the time.
Like Greg said, please feel free to stay in touch, let us know how it's coming together for you and ask any questions needed. Best of luck to you, hope it all goes smoothly.
Patrick