Is there a page limit for my zapptales book?

No, there is no page limit. You can print your entire chat as a book. So that you don’t have to lug around bricks and for the binding to be as crisp in 10 years’ time as it is today, chats with more than 500 pages are automatically divided into volumes. The FAQ point “How are very long chats divided into volumes?” tells you more about how exactly this is done.