Wish I had skipped the Frankenstein and mini PC steps.

Here's two reasons enterprise servers are the way to go:

• Remote management is awesome. Remote KVM, remote serial terminal, mounting ISOs remotely. If your homelab is in a not-so-accessible place (e.g. cupboard or garage), this saves so much frustration.
• High quality rack rails. You're more likely to be tinkering around the back of your server than a company that throws it in a data centre. It's almost like rack rails were built for homelabs.

I wouldn't worry too much about noise. $1000 will easily get you an R730 or T630.