Not sure about NPCs at the moment. At some point you were supposed to be able to get a following of them (like in Terraria), but I don't know if that's still in. They were going to be on the space station, which isn't a part of the game at this point in time. Also, as it stands, upgrading the ship will provide a predetermined number of additional empty rooms. There have been several fan suggestions to add purchasable prefabricated modules with different functions.
I think their usage of "dungeon" just means a "Point of Interest" with dedicated ingress and a treasure or objective at its juicy center.
