Need help making workshop building

UPDATE: so I managed to stip it down enough to get past the “too many materials” problem. However while walls are solid the floors (made with the “box” option) are not. Please advise.

So I created a building Sweet Home 3D (free version). I exported to .obj and tried importing that obj. Ultimately, I want to make it enterable (and then make several more).

In SH3D , I used boxes for floor and roof, added walls, and used a handful of other objects- tub, shower, sink, and kitchen cabinets.

I have three problems:

  1. I can’t figure out how to move the darn viewport. shift+f isn’t doing anything, Everything online says this should enter fly mode, but it seems to do nothing.

  2. I’m trying to follow this guide:
    but when I click on an an object and press y, nothing happens. Dragging to select also doesn’t appear to be an option. I just have a white cursor. I have Blender 2.81

  3. Since I can’t get Blender to do what I want, I tried uploading the .dae as-is so I can at least use t building as a static prop until I can figure out how to actually make is usable. I get an error that there are too many materials. At no point in time do I recall ever choosing any materials or textures for anything. It’s all just white shapes. I don’t understand what this means or what I’m supposed to do.

the .sh3d file
the .obj file
when exporting the .ovb this .mtl file was also created
the .dae file

I’m trying to create a, and the only way I can think of that makes sense is to use workshop models to reproduce duplicates of recurring buildings that I can then decorate (at least until such time as we maybe get the ability to group all the materials in a building and copycat them all at once as a single object, which is unlikely to happen in the foreseeable near future)