I don't think Larian Studios will not do DLC's for their games, so you should not worry about that.
The only DLC's that will be available when releasing the game is the digital stuff like art book, soundtracks and so on or other kick starter rewards for people who have not kickstarted the campaign. Also once the game is released it will be around $40-45 and may be extra for the digital stuff.
Though about expansions? I am not sure as they never done one I don't think.
