Thanks for all your work with the book proposal. It seems like you have a great existing network within you field, this is great news.
I disagree about the readership. Of course, anyone can read your book, and no one would be more please then me if everyone does, but as a target group, this is too broad. We would need to narrow it down in order to make ourselves and your book visible in the noise that is the world today. Let’s start with reader personas: Imagine one reader of your book, and write down everything you know about her: age, location, occupation, educational level, personal interests, family situation, finances and what other books she reads and why. Should this person be real or fictional? Fictional and realistic.
When you are done with this, make another one, another fictional but realistic character that would be interested in buying and/or reading your book (remember that some people buy books as gifts, and that some people borrow books from libraries). When you have four and five reader personas, find them in the real world and interview them!
At this point, we can work on a more defined target group together.
You can find a reader persona template here.