I’ve tried proxmox! Don’t currently have any hardware to run it but excited to do it. Part of the reason I don’t want to put it on the mini PC is that I can’t connect 3.5" drives over sata. I want to use the PC I plan on building as a combo server/NAS.

I am planning on a lot of services, but we’ll see about the rack of servers.

No, off the shelf routers are usually ARM and opnsense is x86 only.

There’s support coming for wifi 6 Qualcomm Atheros chips. The images are still in the snapshot/release candidate stage, so not a full release yet, but they are working.

There’s a lot of used mini PCs from Dell, HP, Lenovo that go for cheap on ebay. Those are a good alternative.