Armor Coatings
Honestly having preset color layouts is very stifling for people who enjoy in-depth customization. Taking a page out of warframe’s book I believe colors should be monetized through color palettes and paint finishes. Everyone starts with a default set of colors that they can apply separately on any part they want. If they want more colors they will have to earn or purchase color palettes that will unlock new shades of colors for them to use. An additional monetization could be paint finishes. You can apply them to a part to make them look matte, metallic, damascus, etc.
Armor Cores
I feel having one core, and just letting people mix and match mk7, mk5, yoroi, etc. would be pretty liberating though I believe clipping would be an issue. Plus I would probably buy more bundles since I don’t have to worry about which core I am getting it for, I can always use them.