The fact that Ultron will be in Avengers 2, but Ant Man won't be introduced till his own movie after that...it confuses me. I hope they know what they're doing. Really anxious to see how they pull off the ant man movie. I think since he's lesser known, it'd attract more ticket sales if it wasn't a stand alone film. People that don't know him, but see him interact with the other Avengers (cameos) in the trailers would probably be more inclined to see it.
Whedon stated that they are going to give Ultron a completely new origin story for the movie. I have a feeling Tony Stark will be the one who creates him. In all honesty, it makes sense. Not a lot of people know who Ant-Man is while Iron Man is pretty universally known.