Hi there @Techvet! I was actually the one that worked on the setup we had at our booth at CES, where you see the trees and mountains. Yes, I believe most things were O scale, and some HO scale. I bought a lot of things from the local model railroad shop. I got trees, two plastic molded mountains, some buildings, and then a bunch of Lego buildings as our landmarks. I also used a vinyl print of the road, so that we could get a single consistent piece to lay down on the board. It was a pretty large print, so I worked with a banner printer, then cut out the road by hand from the vinyl banner.
The actual floor of the "Zumi World" was 2 wooden boards wrapped in a green cloth and stapled to keep it taught.
Hopefully that gives you some ideas!