I haven't responded to this site for for a few years, maybe more, but this thread caught my eye.
I've done large coffee table books, always in a horizontal format, `though the photographs are of mixed sizes.
Now what I am suggesting is my and the participants preference, so don't think i'm posting this as the holy grail.
To me a book that is based on imagery should be like editing a movie. If the images are compelling, placed in an order that makes each viewer turn the page and be surprised, I believe any crop or sizing is important, as long as it makes the viewer study at each image. I also believe the use of white space is important and some are with a an image and a brief explanation of what, where the photograph was shot, or what motivated the artist.
This personalizes each spread.
I did this book for a group of very good photographers that are friends and great photographers I respect. The image below is a comp with just my work, because I don't have the rights or copyrights to show other photographers work. I am only showing it to illustrate what different cropped images look like in a book format
I don't believe there is any rules except keeping some white space around the image unless it can cover a double truck and needs the size to be understood.
Best of luck Alan and the only thing I would suggest is make the book large and do some trial printing yourself on maybe 5 spreads to see if you like the results.
BC
I'm currently in the process of putting together a coffee-table photo book. Around 50 pictures. It's for personal use only. Any recommendations to consider with the book such as leaving borders or not around the pictures of going full bleed to the edges, cropping so they're all the same size and shape, or not to worry if they're different, etc?