Bowker.com

Is there a way to break Fiction and Biography sections into sub-categories (i.e. General, Sci-fi, Large Print, Mysteries)?
Unfortunately, no. Wilson data is only structured by fiction and biography, then organized alphabetically or by author.

Is there a unique identifier for the ISBNs?
Yes, when you click on File Download and select the ISBN-13 file, the first number is a unique identifier, the 2nd numbers are the 10-digit ISBN, and the 3rd numbers are the 13-digit ISBN.