Yikes! Where do you start?
I've been working on a heritage album for my mom for just her side of the family. I only have pics going back to my great-grandparents as children and she wanted me to start there. I did her father's side first and I'm now starting on her mother's side. Even this has been challenging.
I don't have any advice. We have a family genealogy book that was put together a few years back from a far removed cousin in the family and it is SO confusing.
Maybe start with pages that will have photos of more immediate relatives (like ggrandparents) and work forward like I did to get it started and then figure out the really older stuff.
You're really talking about undertaking a genealogy book and that's HUGE.