There are indeed many requirements when submitting nonfiction. It took me most of a day to put it all together, even with photos, as requested.
I seldom find nonfiction publishers that require agents and many are looking for book proposals as well as completed manuscripts. I like the publisher I just sent my query to as they seem to be looking for someone they can work with to get a book just right. I need that. I've gotten comments across the spectrum and just don't want to keep rewriting haphazardly.
Ann, I realize your info was about agents and fiction, but I have been able to use much in querying publishers and nonfiction. I really worked on my platform, speaking of those works I got paid for as well as education and other accomplishments.
I have improved in this process and am hoping it pays off in finding a publisher.