Won't be 1500 pages, LOL. Probably won't even be as long as my Hildebrand book. When putting together an original work on which nothing or very little has previously been published, you'd be surprised how much research can go into a single footnote. All that work last week on the Blackfoot Rangers-associated materials will probably only fill three paragraphs or so.
And the research I'm pursuing right now is for two different works, the one taking place in 1862, and another in 1864. There's a vast amount of overlap involved regarding the same people and same places, so there's that common thread, but for two totally different important stories. As I get into a zone regarding one of the subjects, I follow that thread into the other era and completely exhaust the line of research so later on I don't have to backtrack, or risk losing my grasp on it completely and have to try to recover it later on.