Pretty much, yeah. You start the DLC by going to a specific location which gets marked on your map after you get the DLC.
If you can't afford all the DLC's then I think sailing the high seas and pirating the GOTY edition of the game is justified, they really add to the game. But even without them, the base game still has a toooooon of content that you probably missed your first time through
And I agree with >>14625
, after you've exhausted all the content in the game + DLC, the DUST mod is a very very good follow-up. Modding in general is a great way to inject life back into the game, the community is still very active to this day, and not just the big booba sex crowd