For what might be learned from it, I am just near the publishing of a substantial book of large format having many pages and lots of color illustrations, and I used a hybrid approach a self published version that could have been released as is, but was them submitted to expert professionals for translation into a book. What a difference that last , and rather expensive in time and money , step have made. I feel confident that the book, already somewhat stunning according to some professionals who reviewed my paste-ups, is twice as good from what they brought to the matter.
1. It is my experience that producing a book only begins when the manuscript and the illustrations are in hand, and that there is a sort of magic that employing a skilled professional book designer can bring to the endeavor at that point that must be experienced to be appreciated, and then causes you to look quite differently at most new books that employ illustrations forever after having ones eyes opened as to just what these people can do to take a book to the next level.
2. Hire an editor/proofreader and listen to them.
3. One very handy tool in developing a new book that provides a chance to get some "look and feel" before the final printing is to use one of what I will call the photobook publishers , but in the custom mode; submit to them JPEGS of your final pages from which they can make up some or all of a sort of preproduction version for a modest figure. It is cheap insurance indeed to see how you creation might look, and to have a chance to play with alternatives like different page formats, etc.
Karl