The only things that *have* to be filled in or the archive won't let you upload are title, summary, and rating. You can leave the warnings, genres, and universe info fields blank and still upload (otherwise, people whose fic had nothing in it to warn for wouldn't have been able to leave the warning field blank).

Genre and universe are optional, as are most of the warnings (rape and "Steve or Tony dies or is dead in this fic" are the only mandatory ones, though they're mandatory in a "because we say so" sense, not a "because the site coding compells you" sense).

is it possible to add a "Whole Story" button to the archive, so we can read, print or save a multi-chaptered fic as a single piece?

I don't know (I can't do CSS code, which is why the metadata is my job) but seanchai is going to look into it, because that's a really good idea.