Putting Catalina on the OptiPlex, I would put Big Sur, but I'm not a fan of the UI.
The plan is to have W10 (possibly the Enterprise LTSC version)/Win 8.1+Classic Shell/Windows Server 2019 (through my college), Catalina, W2K(?), W7(?), and a Linux Distro (privacy oriented) running on it. There will probably be at least 3 OSes.
For the record, I'm doing the hackintosh part in Mexico.