Yes Korriban is a vital location because of the True Sith. Ajunta Pall, his ghost, gives some interesting tidbits about it. Even on the loading bar it says that Korriban was the homeworld of the Sith before the first fallen Jedi came.
Yes to Dantooine because well, it's Dantooine and it's one of those places to meditate, if you are a Jedi. It's like the staging ground for the good guys.