I’ll try to answer a couple of these.
Q1 Verify that a disk image’s data isn’t corrupted using Disk Utility on Mac - Apple Support
On second read that link isn’t as useful as I thought. One check you can do in Disk Utility is performed by selecting each drive and clicking on Get Info.
Q4 Yes, some can use either or both
Q5 It’s possible depending on the damage and, IMO, it can be prohibitively expensive for most individuals. I used Drive Savers three or four times between 1999 and 2018. Seems like the cost of recovering a 4GB SCSI drive was around $2500 in the early 2000’s.
Q8 I don’t generate a ton of data these days so I prefer Samsung SSDs for local backup. I do have a lot of experience with Time Machine and no longer use it. TM has been discussed several times on this forum, you might find some of them informative.