If you mean book two, apparently early 2012
Explore chapter one and then you should be able to move onto chapter two.
Chapter 16 of Harry Potter and the Prisoner of Azkabanwas released on the 31st July 2013.
Chapter 5 of Harry Potter and the Chamber of Secrets was released on the 18th September 2012.
Chapter 5-11 were released on the 18th September 2012.
You don't really do anything in chapter five. You just go on to the next chapter.
No you can't. If it isn't an important chapter you can skip it, but if it is a compulsory chapter you have to do it before you move on.
The Pottermore Wiki contains guides which goes though each chapter and also contains lists on every collectable item.
Chapter 5 was locked for a long time as it had not been released. It should be open now, if you still can't access it make sure you have completed chapter 4.
You have to finish all the stages in chapter 15 in order to move onto the next chapter.
Yes, you can find many things. For a guide per chapter see the Pottermore Wiki.
The first new information released about a location was Number Four, Privet Drive which can be unlocked in the first moment of the first chapter.
Yes, Pottermore allows you to explore all of the seven books in the Harry Potter series. Currently six of the books have been released on the site. Please note: only excerpts are posted from each chapter not the whole book.