I built homebrew desktops using Antec tower cases and Intel desktop boards
for many years. The last was based on a Sonata chassis with an included 500
W PSU. It's very easy to add/ remove drives and has low noise features --
the four internal 3.5" drive bays feature vibration isolation grommets, the
main cooling fan is large diameter with selectable RPM, the PSU fan is speed
controlled, etc.. An Intel single-socket ATX server board and Antec
"silent" tower chassis would be a good starting point. I would buy a new
chassis, rather than used; so that no parts are missing.