You could easily throw the components into an old tower case.

Getting the PSU to fit could be a bit tricky due to the rather short cables.

Workstations, like real workstations, are another beast and not what’s typically referred to as “office PCs”, those are indeed rather sff builds.

Again, optiplex sff 3060 as an example, it has two SATA ports, one x16 and one x1 (I think) PCIe, and looking at the PCB, apparently there’s a version with m.2 slots. Sure, not exactly server grade storage, but if you manage to find some version with m.2 slots or invest 10€ for a cheap SATA card, you can get enough storage attached.

GPU wise, absolutely no idea. My optiplex has a wx3100 that I got for cheap and its self reported power draw never goes under 5W, but since this machine is a desktop, it doesn’t run all day.

Sorry, but you’re either pulling those numbers out of your ass or haven’t kept up with the real world for 25 years.

The numbers I’ve posted above are measured using an external meter. I’m German, I have a vested interest in knowing how much power my devices pull.

And you don’t think, office PCs pay attention to power consumption, given they are intended to run 8h a day?

My optiplex sff runs at about 10-15W in idle, and it’s an i5 6500. The t variant in my elitedesk runs at 5W.

“Even deader internet theory”.