Wow! Thanks for all the great advice! :D

Now I just need to figure out:

1. shall I drill a hole in the bottom of the closet for the Ethernet and power cables?
2. can I power the HDDs with a “detached” PSU that was originally meant to have inside a chassi? But then, the Pi doesn’t have SATA connectors… But maybe I can find some extension card than goes on top of the GPIO pins? 🤔