I do see room for a rack. Perhaps a couple. You could use a wall mounted enclosure or two mounted on the studs either side-by-side or on top of each other or a larger floor unit. For this “closet” setup and it mostly being open networking I would lean towards a full height 2-Post network (telco) rack on wheels. Rack mount equipment that you can otherwise use shelves for the remainder of things. For my “small” devices I bought a DIN rail enclosure and added that into the 2-post rack and then I use DIN rail plates with those devices attached.
I have a good resource for the din brackets that work well for small devices of various sizes and custom one’s for rPi units as well that we helped design with the manufacturer.
As for the server you could also place that on a shelf in the bottom of the rack.
For the UPS that depends on size/type. If it’s not rack mountable then put it on a shelf even next to the server. Otherwise you might look into multiple smaller UPS units that can be placed near gear or multiple smaller rack mountable UPS. Some go for giant UPS but I prefer going with multiple smaller units as the goal is safe shutdown not running for days. If you want to run for days get a diesel generator
If you wanted to go full bore you could remove the shelving and have room for one perhaps 2 side by side full (4-post) racks in that room against the wall. You could then back-feed cabling out of them as I think you need access to things on the other side of the wall?
For the IR that depends on if you’re needing to Emit (send) IR commands to devices or if you’re receiving the commands and processing on the control system. In general cases Global Cache devices work great for this and are network attached even Wifi with some.
[EDIT]: A couple more thoughts.
After looking back at the small box devices and hubs I’d definitely use a DIN Rail mounting for things like the HE boxes and the Collective Core box rather than it being hooked up on a stud like that. I use DIN Rails with plates for my hubs and boxes and I’ve never had a problem with signal like the claims from other hubs.