Painting

Acrylic thinner is water based.

As the old saying goes oil and water don't mix...

Try a can of Krylon Gray Primer. Shake thoroughly and apply lightly. If that is to grainy, go to the autobody/autoparts store and try a spray white or gray lacquer- the fast drying kind.

Also, always paint the hard to reach parts first. I am usually airbrushing architectural model parts which include a large number of inside corners for windows/openings. For instance, for an elevation full of window openings I aim paint to the four inside corners first. By the time you are done with that, the overspray will have just about covered the flat surfaces. If you paint the flat (easiest) surfaces first, you will wind up with too much paint on them by the time you get the inside corners done.

Depends on what is available.   Acrylic thinner (Polyscale/now Model Master) and Brush Cleaner that I use is from Badger Modelflex.   A lot changes,  Badger seems to be pretty consistent over the years. Testors, Polyscale/Model Master has changed, moved away from the model train industry.