Help with CPU (and Motherboard) for first build


I’m looking into my first build for a home server.
Basically I’ll be running a Plex server for 2/3 concurrent streams max, some related services and a bit of storage for backups an for the library.
Ideally it should be relatively quiet as well and not incredibly power hungry. My plan was to have it in a 4U case on a rack.

It looks like the NK4 should fit the bill.

While looking at the different builds I found that sourcing the CPU is quite tricky. I live in Europe and most of the Ebay stuff is shipped from far away with exorbitant shipping fees and import duties.

What have other people done? Should I be looking elsewhere other than Ebay? What is a good place for sourcing CPUs and which models should I be looking for?

Alternatively, is there a “new” (as in commonly sold by retail stores) CPU that is a good fit for a build like this? What about a motherboard?

Sorry if this sounds like a lazy question, but I promise that I’ve done my fair share of research and came up empty-handed.

Any pointer is appreciated