I get that, that was also something I used to like about old servers, but let me float a few of the things that I’ve come to realize through my home-lab career to you:

• Raid is perfectly feasible in consumer hardware. If your motherboard doesn’t have enough SATA ports, you can always get an HBA or a JBOD to support for more disks. There’s really no good reason (that I have heard of) for hardware raid today. Just remember raid is not a backup :)
• There are consumer ATX PSUs with redundancy. However, the only reason for PSU redundancy is when you cannot tolerate downtime due to a PSU or UPS failure, and that redundancy might save you a few hours of uptime over 10+ years in comparison to a non-redundant consumer PSU that you can go out and buy if it fails. When was the last time you had a (reputable) PSU fail on you? What kind of uptime are you targeting? If you don’t have an answer for that, 99% is very easy to reach even on consumer gear, and is a strong indicator that you don’t need enterprise levels of redundancy. 99% is literally 3 days of downtime per year. Also keep in mind that redundant PSUs are just going to gobble more power and increase operating costs.
• KVM features - this was the big one for me. I wanted to be able to perform out-of-band remote maintenance on my servers. Then I took a leap and got a Sipeed NanoKVM, and I haven’t looked back. there are plenty of them out there - PiKVM is another reputable one. When buying old enterprise servers, you often have to pay for the remote management license, and that is just another added cost. Not to mention that they lose support pretty quickly, and you end up running out of date software on one of your most critical interfaces to the machine. A NanoKVM, PiKVM, and others aren’t built into the machine, so they continue to be supported for much longer.

One other thing that I’ll mention and you probably already know - enterprise servers are LOUD - even just a single one can literally sound like a jet engine. That’s not a hyperbolae. If this is your first one, don’t underestimate it. I had my servers in the basement with decent insulation, I used IPMI to throttle the fans back to 10%, and I could still hear the whine on my first floor when everything is quiet. If you end up having to turn down the fans due to noise, you’re going to start having heat issues, and then you’re losing out on performance and shortening component lifespan. Noise-proofing a server is non-trivial - you have to allow air flow still, and where there’s air flow, there’s a path for noise too. My current setups all have 120mm and 140mm fans, and I can barely hear them when I’m working right next to them. My 3D printers are the loud ones in the basement now!