Happy Passover to all my Jewish friends and readers. Meanwhile, on the quasi-medieval front, George RR Martin has a new excerpt up on his website from the book we are all awaiting with bated breath. http://www.georgerrmartin.com/
For some reason I have avoided all the excerpts from Winds of Winter, although I know many leap on them. I think it's because I want to understand them in context, so I'm waiting for the full book to come out.
No, each season isn't one book. Book 3 was spread across Season 3 and 4, meanwhile Book 4 and 5 are both crammed into Season 5. This past year, GRRM and the show's creators have confirmed that the show will NOT be put on hiatus if it catches up with the books, and that Season 6 will cover Book 6, and Season 7 will cover Book 7, and that will be the end of it. There's a chance that GRRM may get Winds of Winter out before next year's Season 6 airs, but there's no chance of him getting out A Dream of Spring in time for Season 7. He's told the show basically what will happen, and they've decided that there should be no hiatus because that would mean difficulties with the actors' contracts and in retaining the show's popularity and viewer base. So yes - it has been confirmed, the show will catch up with and overtake the books.