They mean proxmox requires full debian. Pretty sure its not a choice. In VMs you can run anything qemu runs. Also no Docker. The devs are opinionated, not that that is necessarily an issue.
Proxmox is opinionated about how storage is allocated (I think lvm-thin is a bad idea), doesn't support docker, and has some quirks about getting the apt repos set up correctly if you're not a paying subscriber. It's fine if you want to use things in their opinionated way, but know that they're not doing any magic to make KVM work. KVM and LXC are the exact same as you'd get from debian out of the box.
I've been wanting to do something like that, but I was afraid that the combination of LXC + Docker would blow up due to networking or cgroups or something.
Are you running Docker and LXC containers side by side?
Any documentation on how you did it?
I had a previous home server built around docker, and found it fiddly to get right— most of the services I wanted to deploy didn't already have containers, and there was a lot of outer config stuff to play with, getting the containers to restart properly on reboot, getting DNS to resolve them, getting the right data directories set up as binds.
But that was also in 2016, so it's likely things are a lot better now, and conversely, it's not necessarily clear that a VM-based approach would be a lot better in some of these areas.