@thomas.engel - I'm sorry I didn't get back to you sooner. Every so often, my day job interferes with my hobby
It looks outstanding. I believe that you've got the hang of it.
I'm not really sure where your model is located and what scale you're using. While you can locate the XYZ imported terrain where it is natively imported with my plugin, SketchUp sometimes has problems with geometry that is several million meters away from the origin. If you leave it in place, however, and open the terrain group for editing, you can use the Text Tool to select a node on the grid and get xyz coordinates that match your original CH1903+ data:
OR you could move it to the origin and subract the xyz offsets for the rest of your locations. OR you could rescale everything to be in LatLong degrees from the origin. It's hard to say what might be the best approach for you.
The KML file doesn't have the /models/model_nn.dae files included. You can open it for editing in notepad++ or some-such and see xml tags like this:
I suspect that these are your houses ... if you zip the kml file and the models directory into a zipfile and rename it as a KMZ file, I believe it will import correctly. Here's an example error when importing the KML file into Google Earth:
I can't tell from what I can see, so far. However, I generally import more than I need and delete what I don't need.
This is looking really sharp!