Pretty much anything goes for formal these days. We sat next to a man in casual shoes, no socks and an open necked short sleeved shirt!! Most people do however, make the effort and there were many ladies in trouser suits. You'll be fine. I'm not sure about Oceana but you normally can borrow the books for as long as you'd like. We've just returned from Ventura (DON'T EVEN CONSIDER IT) and had freedom dining. We had the same menu as for the set dining restaurants so you still get the formal menus (although they were laughable) in the Freedom Dining restaurant. Am sure Oceana is much better than Ventura. I couldn't be worse.
O'h do dress up it's lovely. We went with Island star once (informal) we hated it, a man dressed in sandles and shorts and T, to dinner whereas I had a cocktail dress on and felt really overdressed and uncomfortable. Formal cruising is not for everyone as you have to have formal wear (it all costs)My in law's has just done their 1st cruise (Royal Carib) and loved it, now she's aiming to purchase some formal dresses (in the sales) for when they go again. I love to wear dress trousers and changes of sparkly tops, also long skirts. If you're short you should try fan tail type cocktail dresses to give the impression of height (you know short at the front, long at the back)
Library: I have seen folk curled up with a book on most ships, I don't think it matter, but I have never been on your ship.
I wear smart/evening trousers on formal nights with sparkly tops, so don't worry about having to wear dresses. If the dress code is formal whether you are on freedom dining or not you are expected to follow the dress code for that night. You can borrow books from the library to read during the cruise as you would any normal library but if they are not returned before the end of the cruise you are charged but this is explain in the information in your cabin. I have always found they have a good selection fiction, none fiction biographys etc even books on dieting (no way whilst on a cruise).