I'm not sure if those are related - couldn't a Ceph node use two SAS controllers? I haven't set it up so I'm not aware of caveats.

Hm, all of their enterprise hard drives are SATA. Those don't support multipath...

They were running it in a DC environment, you should be able to just buy a set of standard AC power supplies and swap them out. These for example https://www.ebay.com/itm/126123732854

Well your host management interfaces shouldn't be exposed to the internet. Use a VPN if you need to access it remotely.