Try spraying it with Plastidip transparent spray after the painting is done. It's transparent rubber that prevent chipping/flaking. I've been using it for year, without it I would not be able to paint soft plastic minis.

After this a layer of matte varnish is recommended as it's pretty shiny.

Thanks for showing, So I need lots of preparation. I think if much better if I hire boston house painters than doing it by myself.