First, I want to apologize to all of you who so kindly posted comments just to have them not show up! I hope I’ve fixed my settings now to get notifications so I don’t leave anyone hanging again. The comments are there now, so thanks for your patience!
The benchwork for the staging level is now complete. I was worried that I would run out of pieces of 1×3 from the old layout, but now that I’ve built an entire level of benchwork, I’m not worried about that at all. The layout is small enough that it really doesn’t take that much lumber to frame a level.
The next step will be installing the basic wiring bus and plywood for the staging tracks.
This was the trickiest portion of the benchwork because I had to build it around an existing stud wall. The wall does provide a great way to support the layout, though. 
Here’s a look at the benchwork for the two “blobs” where the circles will go and the aisle between.