Started with a Plex Media server - Windows 10 i5 (3rd gen), 16gb RAM, a 6 HDDs attached via two JBOD enclosures. Was a decent system for many years.
Finally - moved to unRAID:
Ryzen 5 3600
ASUS TUF Gaming X570-Plus ATX AM4
Vengeance LPX 64GB (2x32GB DDR4 2666)
NVIDIA Quadro P2000
Sabrent 1TB NVMe 4.0 m.2 (Cache)
Sandisk 16GB Cruzer Fit USB Drive
Antec P101 Silent Black Case
Corsair RM850x Power Supply
4 8TB WD Reds (shucked)
4 4TB Seagates (shucked)
Off-site backup to a Synology 1019+ (3 10TB and 2 8TB WD Reds [all shucked])
I wanted a killer Plex system that could handle multiple transcodes and still have some legs for some VMs to play with. So far, things are going great - just an awesome platform to work with. I can always swap the Ryzen 5 for a Ryzen 9 and/or bump the RAM if needed in the future.