I think we can divide the characters four ways.
MAJOR MAJOR (the ones about whom the most stories are told and who have the most interaction with other characters): Emma, Snow, Charming, Regina and Rumple
minor MAJOR characters (still core cast with stories to be told abut themselves but perhaps also serve as plots for the MAJOR MAJOR characters) : Hook, Belle, Henry, and Ruby
MAJOR minor characters (characters who are not part of the core but have a interactions with the core more than other minor minor characters): Blue, Grumpy, and Granny and I guess Neal but I would bump him up to minor MAJOR in S3.
minor minor characters : the rest of the inhabitants of SB including the other dwarves and fairies.
As far as season 3 goes I think we can safely say that the MAJOR MAJOR and minor MAJOR characters are all going to NL together because they are the CORE of the story as a whole. (except Ruby of course…) You have to have Hook there because it’s NL and because of his dealings with Emma and Rumple. You have to have Belle there because she is a major part of Rumple’s story.