Sorry. I wasn't trying to suggest that you should change the size of the model window for every project. Only that what you asked could be done that way.
Here's an example of the second suggestion. In my LayOut template I have three viewports from a sample or dummy model. Each one shows a different scene in the SketchUp file. (I've turned off the title block and other layers for this.)
Original template
The scenes in my project file have the same names as the scenes in my dummy SketchUp file in the template.
SketchUp file with scenes
After clicking Relink in Document Setup and choosing the project file the viewports look like this.
After relinking and choosing the SketchUp file
I did have to change the scale for the two elevations because my template is set up for furniture-sized projects, not buildings. In this case I just selected both of those viewports and changed their scale in one step.