2 - 3B running Octoprint w/ webcam for my 3D printers.
1 - 3B for various experiments and learning environment (spycam, LED programming, etc).
4 - 4B 2M with POE hats in a kubernetes cluster for learning & development.
I'd like to also recommend https://ipfire.org as a firewall solution. It is a highly secured custom Linux distribution with IPSec and OpenVPN capabilities, along with caching updates (for updating multiple systems, etc) and a whole lot more.
On the home lab automation front, I used to work for Canonical on Arm platform enablement. I had a tower of 7 Arm boards that had individual usb ssds, and all powered by an old 150W power supply that was pulled from a 486. Each was controlled via a serial relay control board and a mini-ITX Intel Atom system with 8-port serial PCI board (1 for the relay, 7 for the serial consoles). Everything was automated through Jenkins, bash, and C (before I learned Python - if I only knew then what I know now). I had them setup to power on, pull a custom u-boot loader from USB host (all systems were on a usb hub connected to the Atom), which would start a PXE boot. This would instruct the system to run a network install kernel with Jenkins generated preseed to image as needed. I think the hardest configuration I ran was to automate a full ceph cluster (1 client, 1 controller, 5 nodes) install.
I've since moved on, and the entire cluster was dismantled. Some Arm boards were given to friends for projects, still have 4. Checkout my blogspot for more info.