On that last pic the cage was half empty
After some changes and before finished. The log thing on the shelf is just a ceramic pot - I got it from Rodipet but they don't make them any more. It's actually a bit small for a Syrian. On the back shelf is just hemp mat with one of the rosewood hyacinth tunnels leading from the house roof to the shelf (Charlie couldn't climb steps any more at that point but could manage shallow tunnels).
The tube across the cage roof is the Savic rat tube which is quite long. I also like rat sputniks.
Yes the shelf is the one that came with the Barney. The ranchhouse cage shelves are quite chunky and heavy - but one that goes full width will be stable as it has screw fasteners on three sides. The long narrow shelf I had on the back did slope down a bit with the weight due to only being supported on two sides - but then I didn't fasten it on properly as forgot to use the washers
You can get plastic corner shelves that overlap quite cheaply. Or make a shelf.
The ceramic toilet - I would see what happens - with our current syrian I had to replace it with a plastic one as he did start digging under it and it was sinking and I was worried about it squashing him - although it's not that heavy and syrians are quite strong and I think it wouldn't have squashed him. Another hamster may not try and dig under it!
I think in the Plaza you could even just have a shelf at one end (eg the house roof with a smaller shelf over the gap between the house roof and the edge) and no shelf at the other end - providing there was plenty of substrate and nothing hard to land on in that area. Or just a corner shelf in one corner and the wheel in the other corner.