I realize your paint of choice is acrylics, but I wanted to share my experiences with you, even though I use enamels. I used to do a lot of work with 1/72....particularly figure vignettes. I've worked with several brands, including Italeri, Imex, Preiser, and a little of Caesar. My method was to pierce the figure base with a long pin, which I would then hold the figure for painting. When finished, I would carefully cut the feet from the base. I never washed or primed my figures, and the paint went on fine. I handled them gently for the cutting and placement, but never had issues of paint wearing off. Some of the plastics are rather soft, while Preiser for instance is hard.
Perhaps when finished you might give them a quick shot of clear dull coat, which would act to seal the paint. I hope you find good solutions to your concerns.