Using castoff hardware is a classic first homelab setup. You dont need an actual server to setup a homelab either. Old desktops do the job well enough. I personally run a cluster of 3 of the small desktops i recommend in my last comment, if slightly beefer models. They work great. This site keeps a comprehensive list.

If you're looling for next steps, this is a great general guide. Id personally recommend proxmox of the options he lists. Its a hypervisor that will let you slice up your physical server into virtual machines, letting you split out services like a pihole/*arr stack/jellyfin/kodi in a very sane way.

Linuxserver.io has a huge list of services that you can host with containers inside those virtual machines.