Guidance needed for a book project

A colleague and I have what we think is a very exciting idea for a collection of edited essays, and we'd like any general advice you might have on:

1) Seeking submissions from other scholars
2) Targeting appropriate publishers
3) Writing the book proposal.

I can't give you information about the book's topic, because that would pretty much be a dead giveaway as to who I am if this project actually does get published. But I'm hoping that keeping my request fairly general means that any responses you give me also will be useful to others contemplating a similar project.