Basic stuff...
It's always a good idea to wash your miniatures with water and soap to make sure any anti-sticky-material from the molds isn't still on the model.
Usually I would recommend Citadel spray paint. It covers in a nice thin layer - as opposed to Army Painter which covers better, but also in a thicker layer.
Always use several thin layers rather than one thick layer. Spray lightly - do the dishes - come back and give another layer. Perhaps place the model in a different way that allows the paint to reach new spots.
Never use spray on miniatures if it's too humid. The spray will catch water from the air and apply uneven.
I don't have any experience with Krylon plastic primer though - sorry

But paint isn't just paint. Some paints are intended to cover uneven surfaces - like paint for radiators. Miniature paint is intended to preserve uneven surfaces aka the details.