I bought all new because used market around me isn’t big enough. I went for Silverstone for the case (both a 4U and a 2U), and Startech for the cabinet. Cabinet is expensive new, but apparently in some places you can get used for cheap.
The 4U case (RM42-502) is for my PC so I have a full size 2080S GPU, an ATX motherboard, but not that many SATA drives, but I know they are selling either mods or other cases in the same form factor. Since temps and noise were a big priority, I went with a Noctua D12L ventirad. Only downside compared to normal case is the cable management that is a bit more tricky imo.