Here you will find the process and breakdown of the scene I did in my mentorship with Alex Beddows.
In order to keep the guideline of modularity in mind, I kept the number of materials and textures to what was strictly necessary, and push as much variation as I could with material shaders. I created the bitmaps in substance designer, and then used a master material with plenty of options to tweak each material instance as needed for the composition.
Nanite (Unreal 5.1) also posed further difficulties: the lack of per-instance mesh painting and any other per-instance effect. This was circumvented by utilizing several world-space effects, including a volumetric texture as a base for noises and variation. This system also was extended to the decals, where I could control the global saturation, opacity and other attributes of decals through a Material Parameter Collection.