Legal Question in Business Law in California

Your first question is about publishing, not law. This is the wrong place to look for the information you want.

Your second question is too ambiguous to answer, since you did not explain how you plan to "use" the celebrity. Perhaps you don't want to reveal too much information about your book on this website. If that is the case, I recommend consulting directly with an attorney.

As to advances, I'd suspect without knowing that it is highly unusual for a previously-unpublished author to receive an advance. It might happen if there were a special, close relationship between the author and the subject, e.g. if you were Tiger Woods' caddie or Bernard Madoff's accountant, but usually no, especially for "pure" fiction not based on insider info about a celebrity. The few new authors I've run across are usually subsidizing the costs to print and distribute their first novels.

As to the second question -- are we still talking about the same book, i.e., fiction? My advice would be that when a book is finished, but before it is published, the author and publisher each has to assess the risk that someone's privacy will be invaded in some way that gives rise to the possibility of lawsuit. I'm sure major publishers all have in-house or retained attorneys that work with their authors and editors on possible risks of invasion of privacy and other issues (originality, copyright issues, etc.) and make an informed decision whether to accept the risks or minimize them through editing or just not publishing the work.