@Keet Thanks for your feedback!
I could have bet you'd be the first (and probably the only) person to be happy about this.
While I was working on this plugin, I had you in mind the whole time.
I warned you that it's full of bugs.
Let me start with what works:
1.

-Transparency doesn't seem to work.

Try this:
- Set the transparency to 50%;
- Uncheck the wireframe checkbox;
- OK.
Bug: the plugin also exports the wireframe portion.
I'll now continue with what isn't working:
1.

- Right-click-drag to rotate the model is a little awkward when we use left-click-drag in the Sweet home 3D 3Dview.

I know that, and it bothers me too. I'll see how I can fix it without messing up the others.

- Do not clear the selection when you click outside the model.

Okay, but how do you suggest I deselect all items? It works the same way with the RoofGenerator plugin.
It does this when the button is released if no drag operation has been performed.
I’ll take a closer look at this.
2.

Add buttons to Select all/none.

That could be a solution.
3.

- It definitely needs the same reload as the roof generator

This means that the objects must be special furniture, just like the roofs. Maybe sometime in the future.
4.

- The current preview is perspective. This means that you can't drag a selection rectangle to select faces on the front, it will select everything. In some future version it would be very nice to have an orthogonal view (flat) and only select the visible faces with the selection rectangle and not the ones behind it.

You're right, but it's pretty much the same with AOI. I don't know how it works in Blender.
I will investigate this aspect of the issue further.
5.

- Very important!: Allow full (vertical) rotation. Currently you can never see/reach the bottom faces.

I know. One workaround I used was to lift the entire object so I could access the underside. I'll try to figure something out, too.
6.

- Also important: add ctrl-Z to undo the last actions.

That's what I'm missing too, but first I need to fix the undo/redo feature.
7.

Allow to add/remove materials. (Even if a new material is not used yet.)

Okay, but that might only apply to the current session of SH3D.
The feature that lets you name faces was inspired by you.
8.

- Add smoothing/flat for the selected faces. Don't invent the wheel again, the code for it is out there in multiple versions.

Where? Give me some directions.
9.

A suggestion: make sure you completely license this to YOU with mandatory acknowledgment.

How? What else do I need to do?
10. Have you tried the torus option for creating bent cylinders?
That was also a suggestion you made.
In fact, that’s how I got started on this plugin.