Unfortunately I do not have any additional info on the state of Plex and Apple Silicon. I am still running Intel Macs, so I do not have much input on using an M1 for Plex other than cost comparison of other options.
So glad you mentioned this. While true this will take up more storage, you are absolutely correct. For every Blu-ray/4K rip I have on my server, I used Handbrake to compress down an SD copy of the movie for remote streaming. Personally my Plex server is for me, and while I do care about video quality, when it comes to my remote users I just want a reliable stream without buffering and without throttling my CPU.
Yeah absolutely, again if you just want to use a NAS for storage, use what you prefer and what fits in your budget!
While I am not experienced with QNAP, it is the same tier as (and sometimes a half step above) Synology. My general thought is, QNAP currently has better hardware options, Synology has a better software solution.
I will say, from what I am seeing, the TR-004 is on the cheaper side of the QNAP range. Be careful not to cheap out too much in certain areas. If you can move up to a series or two in their product line (I think that might be the TS?) you might have better longevity and reliability. Do note some of those systems have limitations with how large of a volume they can realistically handle (especially if you are considering 20TB drives). If you are willing to spend the kind of money you listed in your table above, try to find a middle ground where you are not cheating out on any one item just to fit the budget. The last thing you want is to have 80TB of drives bottlenecked by the NAS itself. (Specifically I am referring to any scheduled tasks the NAS would perform for data scrubbing, virus scanning, misc jobs/task that it would run just to keep your data in tact.)
