GRRM said the series will probably total seven volumes. But it sounds as if he is being flexible about that, in case he keeps getting more new ideas that will result in additional volumes, as has already been the case with A Feast for Crows. He also said that the strange phenomenon of the fantasy world's long seasons will be explained in the final volume of the series.
GRRM said that he doesn't have a "Big Board" or a special computer program to keep all the events and characters straight. He says he does it all in his head, by means of using the brain cells that most people use to cope with everyday life!
GRRM said that his favorite character is Tyrion Lannister, and he identifies a lot with Tyrion. GRRM said the Tyrion chapters are very easy to write, and they seem to write themselves without any effort from him.
With regard to characterization and point of view, GRRM said that for any character who is a POV character he has to find something that he and readers can sympathize with even if the character in question does reprehensible things. He said there is always something he can find, or if not then it just won't be a POV character. Gregor Clegane, for example, could never be a POV character, but Jaime Lannister can be despite his bad actions, because there's more to Jaime than that. GRRM mentioned that Cersei will be a major POV character in A Feast for Crows. I was outraged by this and commented ""You just won't ever leave us any character we can purely hate, will you?". GRRM smiled at that, and that's when he gave the counter-example of Gregor Clegane.
I asked a lot of questions about the world-building involved in A Song of Ice and Fire--why the fantasy world is so earthlike in certain ways, with Caucasians in the northwest, Mongol-like Dothraki in the east, black people and zebras in the south, etc., and why some of the characters even have names from terrestrial languages such as Robert and Richard (Germanic) and Philip and Jason (Greek); his answers were that the earthlike characteristics of the flora, fauna, and ethnic groups were just something he wanted--in other words, no real answer at all--and that he viewed names such as Robert, Richard, Philip, and Jason as "neutral" names with no real ties to any language, whereas he would never give one of his characters a name such as Pierre because to him that isn't a "neutral" name. When I demurred about this, GRRM became rather testy and told me my problem was that I knew too much about languages.
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The last question I asked him was about religion in his fantasy world.
I thought the religious tolerance in Westeros between tree-worshipers and worshipers of the Seven was remarkable. GRRM said there hadn't always been tolerance, and the situation as seen at the beginning of A Game of Thrones was a compromise that had been worked out after much conflict in the past. But this is a situation now changing with the introduction of Melisandre and her fanaticism regarding Rh'llor--essentially, religious tolerance is becoming a thing of the past in Westeros. When Robert Baratheon overcame the Targaryens, he opened up Westeros to all sorts of changes in tradition--thus, Cersei's unprecedented move in dismissing Ser Barristan Selmy from the Kingsguard, etc. Westeros is now in a state of flux.