Light dusted coats do not take sanding well until considerable thickness (,,,if it can even be called that....) is built up. You'll remove too much with almost any level of grit you use, waisting that coat.
Achieving a correct ratio of "wetness of paint to Air mixed" is essential when dusting. You want atomized paint that is exceedingly fine-misted, but it must retain it's 'wetness' long enough to hit the surface and adhere without developing undue texture. Such is manifested by the paint particles drying too much before they strike the surface, and forming spheres that do not lie as flat as desired. They build up unevenly, in clusters if you will, and create hills and depressions.
The mix your using contains a large amount of "pearl to poly". The addition of the RGBY elements will mute some degree of reflection the abundance of Pearl introduces. Will it be the right balance? Perhaps. It does seem like your guessing a bit, but don't stop guessing. Educated and informed guesswork lies behind much of what goes down on here. THEN the testing starts. Your doing what I always do. Try your ideas at "Full Size".