I already said in the original post I plan on sellong off and giving away ~15 of them, keeping a few as spares, and only actually leaving one on 24/7

bare metal machines which take IP addresses, against just running it in VM’s which have IP addresses

Both bare metal and VMs require IPs, it's just about what networks you toss them on. Thanks to NAT IPs are free and there's about 18 million of them to pick from in just the private IPv4 space

Big reason for bare metal for clustering is it takes the guess work out of virtual networking since there's physical cables to trace. I don't have to guess if a given virtual network has an L3 device that the virtual network helpfully added or is all L2, I can see the blinky lights for an estimate as to how much activity is going on on the network, and I can physically degrade a connection if I want to simulate an unreliable connection to a remote site. I can yank the power on a physical machine to simulate a power/host failure, you have to hope the virtual host actually yanks the virtual power and doesn't do some pre shutdown stuff before killing the VM to protect you from yourself. Sure you can ultimately do all of this virtually, but having a few physical machines in the mix takes the guesswork out of it and makes your labbing more "real world"

I also want to invest the time and money into doing some real clustering technologies kinda close to right. Ever since I ran a ceph cluster in college on DDR2 era hardware over gigabit links I've been curious to see what level of investment is needed to make ceph perform reasonably, and how ceph compares to say glusterFS for example. I also want to setup an OpenShift cluster to play with and that calls for about 5 4-8 core 32GB RAM machines as a minimum (which happens to be the maximum hardware config of these machines). Similar with Harvester HCI

It just takes a lot of extra power and doesn’t achieve much

I just plan on running all of them just long enough to get some benchmark porn then starting to sell them off. Most won't even be plugged in for more than a few hours before I sell them off

there is no real reason to do this and I don’t understand so many people hyping it up.

Because it's fun? I got 25 computers for a bit more than the price of one (based on current eBay pricing). Why not do some stupid silly stuff while I have all of them? Why have an actual reason beyond "because I can!"

25 PC’s does seem slightly overkill. I can imagine 3-5 max.

25 computers is definitely overkill, but the auction wasn't for 6 computers it was for 25 of them. And again, I seriously expected to be out of and the winning bid to be over a grand. I didn't expect to get 25 computers for about the price of one. But now I have them so I'm gonna play with them