All of this advice is merely nice-to-have. You can easily just use an old desktop or laptop to do the same. I've homelabbed for a long time and have rackmounte

All of this advice is merely nice-to-have. You can easily just use an old desktop or laptop to do the same. I've homelabbed for a long time and have rackmounted systems full of old desktop parts, rather than buying or seeking out used server hardware. It just isn't required. ECC RAM? Nah. It's useful if you can find it cheap and your CPU supports it but it's overstated as a problem IME. I do agree you should buy 2U or even 3/4U equipment, if only so you can mount much larger (and thus quieter) fans.