Question corrected.

I wouldn't think data is the issue, as error trapping should handle this if you have concerned. You can look for the error and redact the message.

Hold off. The submission needs work. If I don't get an updated one in a week, I'll post here.

reviewed.

backup has never interrupted the log chain. Only the differential chain is impacted with a full backup. Copy only is for avoiding differential issues.

Yes, 16 is small, though how much data? If you have <16GB of data, maybe it's fine and you need to worry more about code and indexing.

There is a good explanation here. It's not 0 byte for nulls: https://stackoverflow.com/questions/3793022/how-do-you-get-to-limits-of-8060-bytes-per-row-and-8000-per-varchar-nvarchar/3793265#3793265

The sparse column thing is for fixed width fields, like int, tinyint,etc