Yes, they're set during the series. I've only read the first two (since the third isn't out yet), but IIRC Greg has mentioned that his is set during the series as well.
This is true. The books are all set around the fourth season or so, when the crew is still in Boston--and presumably before the big season cliffhanger.
My book isn't officially out yet, but I believe it's starting to turn up already. I got my author copies weeks ago, and I'm already hearing from readers who seem to have gotten their hands on a copy.