I’d start with learning some networking basics.
Subnets, default gateways, DNS, routes, VLANs.

Then get another computer to install proxmox on.
Learn VMs, SSH, firewalls, basically Linux. Probably VPNs as well.

Then set up a VM and play with docker & docker-compose.

And that’s most of the tooling to be able to self host anything. A VM with docker, set up the docker compose of what you want, boom: done.
Some projects are more of a “full of” kinda thing (like home assistant), which would be its own VM