Mesh is the precise geometry of the mannequin, disregarding all teams and elements. Teams and elements is how completely different meshes are organized in SketchUp. Different software program may do issues otherwise.
When you have these many textures and they’re actually distinctive (not related or duplicated supplies and textures), one of the simplest ways is to make use of blender. Duplicate the mannequin, take away textures from duplicate, uv unwrap it and bake the textures of the unique into the unwrapped model.
If this appears advanced it’s as a result of it’s, nevertheless it’s one of the simplest ways to do one thing as advanced because it appears by your description.
In any other case, do it manually, should you assume it may be sooner.