Crazy amount of news coming in, Toonzone this time have in interview with Mike and Bryan

Interesting points from this one are

November 2009 was the start of the idea for Korra
Regarding the Books of Korra, Book 1 was always planned as 12 episodes, each book will be more of stand alone stories each with their own villains and resolutions, but there are overarching plots throughout.
In answer to the classic “What happened to Zuko’s mom” question, Mike had this to say ” I don’t have an answer for you at least not yet “, Yet being the key word they have said this in a few recent interviews, which highly suggests that something is coming where we will find out what happened.

So again worth a read in full, though a lot of the stuff you will already know.

Sokka and Hawky