Low hanging fruit: ditch the dumb switches and get a 48 port or something. Place it on the shelf above. If you’re using the two switches to ensure that you have more throughput per machine considering putting in a 10gbit uplink. Beyond that consider mounting/stacking the monitors differently and changing out the wood shelves for metal shelves for airflow. The trick is to know in which direction they dissipate heat. If they’re fanless the heat is gonna go up which will limit your ability to stack.

I don’t want to say it’s the most popular Linux server distribution but it’s definitely up there. Lots of people and organisations are using it.