Used tiny/mini/micro.

Get the gen of Intel CPU you can afford purely for hw transcoding. 6th-8th gen is good, newer gets you more, even av1 becomes an option.

If you have a NAS, great, store videos there. If you dont, I’d upgrade the t/m/m with an m.2 and (config dependant) you can usually stick a 2.5" in there as well.

Proxmox for the OS, run lxc’s for the individual services you want, or make a docker LXC and run them in there. Personally I just make an LXC for each service.