I did both footnotes and endnotes. Endnotes were used for the legal citations, while footnotes were used were I needed to clarify things in the text. For instance, I comment on state supreme courts, and have a footnote that New York's state supreme court is called the Court of Appeals. Ultimately, footnotes went on the pages that they applied to, while the endnotes were all at the end of the book (the could also go at the end of each chapter).
Mainly for the sake of both my eyes and my editor's, footnotes were done in the normal font during the editing stage. They pretty much read as normal text. The endnotes were done in 14pt type during editing. This enabled us to see them a lot clearer. The proofreader especially appreciated it. Then when the book was put onto proofs, my editor just switched everything around to the type faces that she wanted. My editor was experienced with nonfiction and knew had to calculate the end size of this stuff, although she was not familiar with the weird quirks of legal writing.
If you're relying on Word to correctly count legal citations, especially with people who aren't familiar with them, don't. For example, Smith v. Jones, 110 NH 143, 423 A2d 564 (NH) counts as ten words. Normally words average five letters, and if you count this that way, you only get seven words. Problem is this will mean you'll need 30% less space than you estimate based upon word count.
I took a look at the final version (although not the actual book) for EQUINE LIABILITY. I have 10,390 words in endnotes, although only a little over 50,000 characters. It ran for about fifteen pages. That runs nearly 700 words per page, which is one reason why endnotes and footnotes need to be separated for word count.
However, depending on the book proposal, any publisher is going to automatically assume footnotes and endnotes. I didn't discuss them at the proposal stage. Towards the end of the process, the editor and I had disagreements about the indexing. I wanted a detailed state index and she wanted none. Compromised on a reduced state index that runs less than a page.
Best of luck,
Jim Clark-Dawe