Wow, what a nice setup. The building architecture and history seems like a great inspiration for creativity. I'm envious of all the space and the ability to work on multiple projects at once. Looking forward to seeing more projects coming out of your shop.
Nice work, this is super cool. I especially like how your work tables are on wheels and you can reconfigure the layout depending on your project needs. The ability to move your sandpaper racks and rosin paper roll from the French cleat on the wall to your work table is ingenious.
I'm planning a workshop reconfiguration in the near future and I definitely would like to add some of these features.
One option for adding another shelving tier would be to add a shelf above the bottom close hanger rod. If you had available height to bump the top hanger rod up a bit, this might provide room for an additional shelf. That's the nice thing about designs like this, you can tweak them as you go.