16TB of data on a 36TB server, nothing backed up. Advice?

I'm running a plex server on a Windows 10 PC and I'm at the point where I'd like to protect myself from potential data loss. I'm using 16TB out of 36TB total.

I currently store my data on a mixture of SSDs and HDDs using Drivepool. One feature of Drivepool is that it will email me when a drive is removed. I'm very familiar with this because one of the SSDs is temperamental. It's fine for weeks/months, then disconnects randomly. Slide out the tray and slide it back it, and it works again. I would like to be in a position where one of my drives can fail/disconnect and can be addressed at my convenience while my server and its data remain accessible uninterrupted.

I can add more details regarding my setup if needed. There are definitely things I would do differently the second time around, but I'm not necessarily looking to start fresh right now. I do have a singular unused M.2 slot on the motherboard. I might want to add an NVME ssd in the future, then install Unraid OS or a Linux variant.

Any advice is greatly appreciated. Also, thoughts on moving a drivepool from one OS to another on the same system?