I personally had the best experience with mergerfs (Drives can be any size and can be backuped by snapraid) and an external enclosure up until recently. Unfortunately USB is such a limiting factor because of bandwidth and also latency. I can only realy recommend to get a new cheap Server which has Support for sata If you want any usability while Transferring or moving files.
I think this does not mean it has to scan the file directly, but maybe keep all the hashes to files that were taken down and stop them from getting uploaded again. This would also be fairly unintrusive, but could add a few false positives.
using less space for your storage is always better
weird that this took so long i think this probably breaks both of their tos
I personally would recommend this n100 to get a real psu which can add many drives, 6 Sata ports and a standard form factor.
Edit: Also a PCIE Slot to add 10 Gbit Networking Card if dual 2.5gbit is too slow. And if you need more power there is also and i3 n305 variant of these mainboards.
I think this would take way to long to travel somewhere where things acutally live the light will probably only reach them long after humanity is gone.