My current server is a i3-10100 with jellyfin, truenas and a docker VM with 45 containers running for the last 4ish years.

Beyond initial booting or starting a docker stack, the CPU load is low. However if I'm pushing lots of data at gig speed to the nas, the CPU can hover at 80% or more. (Encrypted dataset)

If you're buying new, i'd go with an i5 at least. If you're only going to have a few services an i3 will work.

That said... I've outgrown it and currently waiting on its replacement server to show up.