1) > I would use this paint to practice, if this is a pre-mix, usually a small amount of dish soap (a drop or two) would be enough to clean your air brush
Tamiya makes a good thinner/cleaner solvent, they also make a nice acrylic paint and have a variety of colors. Might be a good choice for weathering, you will just have to put a coat or 2 of dull coat over your work.
2) > You want to use Testor's Air Brush Thinner, this will work with all of their enamal paints. They also carry the "Model Master" brand, same stuff but more expensive.
3) > I like the Model Master paint by Testors because they have a great range of colors, the paint is very durable. The mixing ratios are very simple and they are printed right on the can or bottle. You can use the Air Brush Thinner for cutting and cleanup. This stuff smells, so make sure you have a window open