Those Dell's are up there at the apex of asthetic case design to me. I owned a Dimensions XPS P90 in 1994, and at 17 took it to college where I steadily upgraded it over the years. The case was fantastic to work with.
You mentioned wanting to set them up - will you bake the large duplicate quantities down to a unique set of "best of the best" built systems (with the healthiest parts), and then keep a small backlog of parts, and unload the remainder?
Only asking.. I have two totes holding roughly three machines from 20-ish years ago, that I originally had planned to setup at some point in my future old age. Well.. I'm now that older future guy, and I barely have time to spare for my modern active retro projects (dos gaming on retropie), let alone what my past-self cared about. Plus, functionally speaking, I find the Pi offers far better power, space, and operational-conveniences versus retro hardware. Maybe I needs to 3D-print a micro Dell XPS Dimensions case for my Pi, and call it good 😀 That's just me though.
When you do start setting stuff up, I'm looking forward to more pictures and your thoughts!