Hello, I'm attempting the harmonic scene. So far did the blockout, some lighting and rough color blocking.
As kanga mentioned, worry only about the outside of the garments. The inside of a garment (if at all visible) can just be duplicated of the outer, delete what you don't need, and pushed inwards with a push modifier (stacking UVs as well).
The thickness of a garment could also be done post-bake. The edge highlight of the garment thickness could then just be handled with weighted normals rather than trying to come up with a highpoly of a garment with thickness + inners, and relying on baked tangent normals.