If it's a once-off operation, then shrinking the log (and only the log) once at the end is fine.

The accepted wisdom is not to schedule shrink operations to...

There's no such thing as 'row chaining'. A row must fit onto a single page, the only exceptions being that data in varchar, nvarchar & varbinary columns can be partially...

A restore recreates the DB exactly as it was at the time of backup. If you want multiple files, restore, then split.

Please rather start a new thread for...

2

Simpler. Easier to read. Less prone to mistakes. Doesn't require permissions granted directly on the tables.

Though the two aren't equivalent. The WHERE clauses are different. Did...

It's defaulting to the American format, month/day/year, hence you're trying to convert the 3rd day of the 24th month, which doesn't exist.

Use unambiguous formats (preferred), or use CONVERT...

The new column has to fit on the original page.
If it's also varchar/nvarchar/varbinary, then  it  too can have portions of its data  sent out to row_overflow pages

And...

Availability Groups is a HA solution. The secondaries are up to date with the primary, but either inaccessible or read only

Those suspect page entries are from several months ago. They could have been fixed, or regular maintenance such as index rebuilds could have made them disappear (an unallocated page cannot...

You're going to have to give us a lot more information before anyone can begin to help.