Change contents of "Book outline"?

I'm developing a site where users post stories (Story node) into categories (Books -- I have set up the possible Parent Book Pages for them to choose from). I don't want them able to post stories under other stories (child page to a child page of a Book) and so once they choose a Book, I don't want that other drop-down menu to show up. Also, I don't want them to be able to weight their stories. How/where do I get rid of these options? Also, is there a way to make choosing a Book mandatory? (Right now it just says something like, "You have to choose a category or your story won't show up on the site.")

Lots of questions, I know, and I'm sure there's a way to do it. I'm semi-comfortable in code but afraid of breaking the site by experimenting. TIA!