If SpaceX's Red Dragon will ever bring astronauts to the red planet, would it need to connect to a deep space habitat? I'm asking because the red dragon seems to be too small for a seven or eight month trip to Mars.
They won't. Red Dragon is an unmanned concept demonstrator and experiment transport. SpaceX wants to use it to test Mars EDL (entry-descent-landing) technology and algorithms they develop for their next generation ship (currently known as ITS or BFR) which they want to use for astronauts.