Yes, those are all concoctions that can be used, but why not use the product that company makes that is specifically designed to work with their paint.
Works the same every time, no need to mix something else up. Thins both the Model Air and their Model Color, really is all you need.
Problem with using stuff like distilled water, is that while it will thin the paint, it also weakens the covalent bond of the paint to the subject you are painting...same with windex (the ammonia in it actually breaks up the paint rather than thinning it).
Future...yes, it will work, as it is just basically an acrylic clear medium.
The Vallejo thinner is designed to work with the paint, thinning it, but also aids in helping bond the paint to the subject, and has some retarder in it already to keep your paint from drying too quickly in the airbrush, or on the way to the model.