I hope you are doing 3-2-1 backups now

If you've got a m.2 slot in the mini PC you could add a cheap 5 sata port m.2 and connect them that way. If you don't want to solder power you could really make it a butcher job and hack up the power from the sata to usb connectors.

Sucks to hear about your loss, I've recently lost my proxmox setup and migrated everything to Nixos. My install threw a wobbly, terminal was cooked, could only ssh into some containers so I wiped the install and migrated.

In my proxmox setup I found it easier to mount the drives as lvm to the host proxmox machine and pass them through to lxc via bind-mounts rather than adding another layer of shares / overheads.

I don't think those USB cases are priced realistically at all. For what they're asking I may as well just buy hardware to build a NAS box.

Well specifically I'm referring to the internal hub on your system and how it shares port bandwidth. It doesn't really matter for things like a mouse or keyboard. However, when you are talking like permanent flash disks it's worth investigating how the bandwidth is shared between ports. Specifically the switching back and forth between the storage devices. Some filesystems handle this better than others.

I was was also referring to a way I found that stabilizes the connection. That being a USB to SATA controller via like one port. That way that port tends to take advantage of all the bandwidth without switching around.

Also keep in mind USB flash media is notorious for wear compared to something like nvme/msata disks.

It's possible to combat writes on flash media by utilizing things like ram disks in Linux. Basically migrating write heavy locations like temp and logs to the ram disk. Though you need to consider that restarting wipes those locations because they are living in ram now. Some operating systems do this automatically like opnsense with a check mark.