HI,
That is a good post fair play. One thing I would look at as it has happened me before all be in on a QNAP device is the restore time.
Restoring 10TB could take a while and depending on stripe size, software and other factors you may get at worst 20 mb/s.
Bar that looks good you have the off site and the redundant. There is no one size fits all for DR but you have detailed all your point and answered them well. I think you will be fine.
Would be interesting to see how your "home one wheels" works with mechanical drives :)