I’ve only played with it a little but the architects in my firm do most of our 3D rendering in sketchup so it’ll probably work well for just doing a layout.
Here’s another vote for Sweet Home 3D. I’ve been using it the past few weeks in designing an addition to my lake house. It’s amazingly powerful for an open source CAD program.
Yes, you can scale the wall thicknesses and the furniture.
The one thing that needs to be improved is putting a roof on the structure for the 3D view.
I use AutoCAD professionally, but something like FreeCAD should be good for your application.
IME it’s actually not that great for doing 2D. My recollection is that it is set up for showing objects in perspective, and just getting it to show things flat isn’t as straightforward as it might be.