I’d keep it simple like this: one “hard” socket per bone for all variants, sharing the same pivot and a small box collider. The add-ons using that socket would be grouped into just 2-3 size classes (small/medium/large) instead of perfectly matching every single part - a bit of mesh intersection is fine as long as nothing pops at gameplay camera distance. For colors I’d keep all sockets and brackets on a single neutral material (steel / grey plastic) and only let armor, covers and the main module shapes change colors. On top of that you can have a few fixed palette presets as a base, plus maybe a subtle tint control for one accent color so users can nudge the look towards their project without breaking your original schemes.