Creating new library question

I have many books in my library that are for others and I don't plan to read. I would like to create a 2nd library of just the books that I might like to read. I'm not sure which of the 3 options to choose when creating the new library. My entire library is stored in my dropbox.

Also, if I copy my books from my main library to my 2nd library, will it double the space used or does it just point to the original file?

Would this be better accomplished by making my books into a collection rather than creating a new library?

Thanks