"Mean Green" also called "Simple Green" is available at Walmart, Lowes, and perhaps Home Depot as well as other places, and is biodegradable and safe for the environment and is an absolute BEAR at removing acrylic paint. It strips paint in minutes. MUCH better than brake fluid, and more environmentallly responsible.
If it's lacquer based, you're out of luck Nothing strips lacquer but lacquer, and that will eat your plastic in no time.
I think that you're worrying too much about your primer coat. Unless you're going for a flawless, mirror-smooth, super-shiny coat of paint on a car model, you can have "uneveness" in your primer coat. All it's really there for is to give the paint someything to grab onto, especially if you have PE parts or resin in the build. Your paint base coat is going to cover all that up opaquely anyway, so don't over-react to a few odd primer variations.
The best thing you can do for primer is to buy a big can of Duplicolor gray or white primer at an auto store and decant it using a big straw into a tall paint bottle whenever you need it. You can paint around two dozen full-size models on one big can if you're not wasteful, and for pennies on the dollar of what other modeling primers cost, and it fills very nicely and is not adversely thick. It's not hard to decant it; just wear breathing protection like a triple-step respirator, which, honestly, you should have anyway if you have an airbrush, and understand that you have to let the primer "gas out" for a few hours by loosely capping the bottle and letting it sit. I usually let it sit in the garage overnight, and it's ready to use the next day.