Well, the next 3 books will occupy at least 6 seasons if they all get made, so they are good through 2017 at the moment. I sure hope book 6 is out before then, but there could still be a problem eventually.
I don't think so. The first two books were one season each. The third book is going to be divided into two season. I don't think books 4 and 5 will each be split into two season. It will only be two seasons for both of them combined, three at most.
So much of books 4 and 5 are filler, long journeys, repetitive actions, long descriptions, and soul searching that will be cut out of the TV show. Much of it should have been cut out of the book by its editor.
No one wants to hear, "have you seen a maid of thee and ten," over and over again. Or watch long journeys with drinking and pissing being about the only thing that happens. Or watch the river turtles. Most of the soul searching that goes on in book 5 will be cut; inner monologues won't happen in the TV show.
You won't have all the descriptions of urination, bowel movements, and menstrual cycles that make it into the book.
"Every stool was looser than the one before, and smelled fouler. By the time the moon came up she was shitting brown water. The more she drank, the more she shat, but the more she shat, the thirstier she grew, and her thirst sent her crawling to the stream to suck up more water." -ADWD