I use TMM. Tiny MediaManager.

It can be used for free with limited functionality. Or you can pay in order to get full functionality.

Very compressed low bitrate 4K may be much worse than less compressed high bitrate 1080p.

I prefer to collect REMUX copies of movies I really like.

Then you have to assume that the file already is at least a little corrupt. What you need to determine is if the level of corruption is so bad that it is a problem. If it crash an audioplayer or the file sounds bad. Ideally you have a backup copy that is better or you can download or create a new file that works OK. Possibly you can re-encode the file to fix problems. It will degrade audio quality if the encoding is lossy. But perhaps not enough to be noticeable.

Some audio file formats have embedded checksums. FLAC or WavPack. Perhaps more? You should be able to find utilites that can compare the embedded checksum with the current stored data.

In the future use a checksummed format or store separate checksums. Or zip the files. The zip format has embedded checksums. (Same with all(?) other compressed formats.)

It is important that you check to see if the file really is pristine after you take the first checksum. That you can read and use the file. Otherwise you may take a checksum of a file that is already corrupt. That is not very useful.

Most likely it is not actually spontaneous bitrot. It is much more likely that somebody made the file corrupt. Usually it is some form of user error.

It is a very good idea!

A friend. Make your friend hoard data. And share it with you.

Otherwise large HDDs, at least 18TB, are most likely still the cheapest per TB. If you mostly write once and read much, much more, then SMR is fine. As long as it isn’t in a RAID array that may have to be rebuilt.

SSD is, I think, better in all ways, except price and capacity. So SSDs are very bad for bulk storage.

Multiple backup copies on different media, stored at different locations, is how you reduce the risks of data loss.