Used business desktop from eBay is what I run. With what you want to run, you’ll be fine with even 10 year old hardware. I’m running a dozen services on 10 year old basic business hardware with no issues. With regards to media though: if you’re not getting a dedicated GPU, get a Intel 7xxx or later CPU so you have Quick sync for transcoding.

I run Ubuntu Server on one, proxmox on another. Both have their pros and cons. Depends on what you want to do. If your plan is just to run everything in containers (and it should be), Ubuntu with docker is plenty. If you plan on playing around with VMs, go proxmox.

As for what services, here’s a huge list of different self hostable services grouped by category/function: awesome-selfhosted.net Most have a demo site or a quick install guide for docker that makes it easy to try stuff out.

Avoid selfhosted email if you can… it’s a whole different animal.