My go-to for “server” hardware:

• Old office desktop: Dell Optiplex SFF, HP Elitedesk SFF, Lenovo Thinkcentre SFF
• CPU: 7th, 8th, or 9th gen Intel i7, preferably something with vPro (really neat OOB management - keep it local)
• RAM: At least 8GB
• OS drive: 256GB SSD at the minimum
• OS: Debian
• Media storage: Something large enough to store your media. 3.5" HDDs are great for this, but SSDs are better if you can get your hands on a large one.

I also have an old HP Proliant ML110 tower server case from 2004 that I outfitted with:

• Rosewill 3x 5.25" HDD enclosure w/ 4x 3.5" hot-swap bays (getting another one soon for the lower bays)
• ASUS Prime Q270M‑C motherboard
• Pentium G4560T (7th gen/Kaby Lake)
• 8GB DDR4 RAM