It really depends on the type of entries you have. Qeepsake Books max out at 300 pages.
Do you have long-text entries with lots of photos? You might only be able to fit ~150 entries in a book. If you have very few photos and short-text entries, you might be able to fit 400+ entries in a book.
You might have to play around with the date range tool to figure out how many entries you can fit in your book.