I've got a 36U StarTech rack full of Supermicro chassis/motherboards and miscellaneous other things (Cisco switch, KVM, monitor, etc). The initial cost was pretty expensive but, the rack will last forever and the chassis will be useful until the SAS backplanes start to fail. In total the rack has around 100GB of RAM, 40TB of disk and around 30 cores of varying capability (everything from Intel Atom to Intel Xeon X56xx) and a lot of UPS (rack stays up for 1.5 hours without power). It's been up for a few years now and, though it's crazy stable, I do have some observations about a "home datacenter":
The rack sits in a 100sqft room on the main floor of my house and it presents some challenges: 1) A 100sqft room is likely to have a 15 amp breaker. The machines in my rack are all pretty power efficient (500W at idle) so, I'm not regularly bumping up against the 80% load of a 15 amp breaker but, it's something to consider. 2) Cooling. It can be a gigantic pain in the ass to keep the room at a sane temperature. In the summer, I have to open up the window and put a window fan in it. In Spring/Autumn, I generally monitor the drive temps and open/close windows as needed. In winter, I could open the server room door to heat the house except: 3) It's loud. Like, really loud. I've replaced all the power supplies in the big servers (which all have redundant power supplies) with super-duper-platinum-efficient power supplies and, it made it a huge difference but, it's still very, very loud. I bought a solid core door for the server room and put audiophile type sound absorbers in the room. It's still loud.
Apart from those 3 things, having a nearly-enterprise level rack in your home is doable. It's a lot of upfront money and work but, once it's all in place, it's pretty easy to maintain.