Really nicely done! I'm part of a viz team in a large architectural firm, and we have started to pick up a lot of Enscape work in a similar fashion to this. It's interesting to see how two firms a world apart can end up with very similar workflows!
With regard to your issue with SketchUp slowing down; we have adopted a similar workflow to the typical Max + xref pipeline. We split our Revit models off into various worksets, import those into SketchUp to particular layers/tags, then xref these sub-files (per building babsis usually) into a master file. It means we can have multiple artists working on the various sub-files, while the head artist works within the master setting up cameras, getting the lighting right... all the good stuff. It relies on careful layer/tag management in the files, but we are pretty good with that now. The one issue we have had was Enscape's questionable proxy appearance, but we are going to trial using Transmutr to get around this... not a huge deal as we compose everything within Enscape anyway.
Lastly - how are you importing your Revit files? We found the texture scaling issue was only present with FBX, whereas if we brought in DWG, while it didn't have material information, the mesh quality was much better and instancing was present. We used an FBX import to "grab" the materials and save them to our library, then apply them to our DWG import using Thomthom material replacer. Most Revit textures and UVs, as you pointed out, are hopeless anyway!
Great work, has got me inspired for our next job with Enscape.