[drMerry]

The sorting-option is the only thing I need. If it can be done simple without a column, it's fine (great) to me.

Next group is not an option I used at this moment. I use the mark option so had no need to hit next.
I will try it.

Your last problem.
If books 1 and 2 are duplicates and 1 and 3 are duplicates. 2 and 3 will be (just like 3 and 1, 3 and 2 and 2 and 1) Isn't it?
That's why I think it is no problem.
Also, if you would like to sort on number of duplicates, where would you put 1 in your case?

EDIT:
It does remove with ctrl+\