Today back to work again. To share my experience with the layer issue. Yes, I also got surprises of visible surfaces in KS3 that were invisible when I exported them from WF5. In my situation it had to do with an mother merge part the still showed her blanked layers. In the end I was able to control, and only exported what I wanted to see in KS3. However it was more complicated to handle, which I had to do in WF5 (not in KS3). Before it was so easy from WF5 to KS2, just what you see is what you get (including the surface colors).