I highly recommend anyone going this route to use Proxmox as your base install on the (old) hardware, and then use individual LXCs/VMs for the services you run. Maybe it's just me, but I find LXCs to be much easier to manage and reason about than Docker containers, and the excellent collection of scripts maintained by the community:
https://community-scripts.github.io/ProxmoxVE/scripts makes it just as easy as a Docker container registry link.
I try to use LXCs whenever the software runs directly on Debian (Proxmox's underlying OS), but it's nice to be able to use a VM for stuff that wants more control like Home Assistant's HAOS. Proxmox makes it fairly straightforward to share things like disks between LXCs, and automated backups are built in.