Should you try to read every single book? If you really want, but a lot of books can and will make your head spin if you do not crack down on its purpose and what it's trying to tell.
Otherwise, http://www.imperial-library.info/. Every single in-game book, Pocket Guide to the Empire (great for background information, and was given in the TES games), and obscure text (don't read till you understand the in-game books that deal with myth and metaphysics). The big thing that'll help prepare you for Skyrim is to read the pocket guides, books on religion/myth of TES, and hanging around this section of the forum and read the discussions.