Welcome to the club!
My Plex box is an i7-950.
Not a 9600k...
It's whatever I had lying around.
It eats more power than it needs to, but it fits a whole lotta hard disk, so I'm good!
It also shares it's library with a little VM on a Dell tiny i5-4570t which runs jellyfin.
I prefer jellyfin, the Mrs and the MIL prefer Plex.
Don't stress high end hardware, just make sure you can stuff enough disks in it to hold your library.
I bought the tiny used from an auction, and I built the Plex box back in, like, 2008 or something?
Anyways, the point is, it'll probably work fine, go cheaper if you want.