Using endnotes instead of footnotes is acceptable. You placed your endnotes at the end of your book, which is excellent. You could also include endnotes at the end of each section of your book. It’s up to you. The only disadvantage of using endnotes instead of footnotes is that the reader will have to flip back and forth between the page he’s reading and the endnotes’ section of the book if he wants to know where you got the information. On the other hand, using endnotes makes a book look more as a novel and less as a historical essay. Depends on what you want your book to be: a novel, an essay, a thesis… It also depends on what type of readers your book is being written for: nascent readers could be scared of reading a book which would include footnotes at the end of several pages, whereas academics and historians are fond of such footnotes. Appearance is of the essence, as much as substance. I personally prefer footnotes.
One thing to remember though: the endnote must mention the source’s specific page(s) where the information was found. Hence, you must not include the source’s total number of pages in a footnote/endnote. It’s only in the bibliography section of your book that you’ll specify each reference’s total number of pages (i.e.: for a book, it could be “256 p.” but for a review article, it would appear as “pp. 15-35”).
Regarding the number of references included to your book, remember to include an endnote only when required and don’t worry about the total number of reference notes. Do not add any unnecessary notes but do not cut any if they are required. History is a science and we must respect a proper methodology… endnotes’ included.