Your idea of the concept is nice, but you're missing out some details.
The end scene of the Avengers with Thanos, is a cosmic threat, this is actually the villain for Guardians Of The Galaxy (this is referenced "cosmic threats" for the description of Guardians Of The Galaxy movie plot).
In Iron Man 3, the kid that Tony Stark meets tells Tony that he could add these gadgets into his armour that would make him become stealthy, which Tony Stark says "You know what? That's not a bad idea". Unfortunately we don't see the stealth mode for the rest of the movie.
At the end of Iron Man 3, Tony destroys all of his suits, and has surgery which removes his chest reactor (so Iron Man no longer exists).
However, one suit survived. The Iron Patriot suit.
So I believe that in the Avengers 2, the Iron Patriot suit becomes Ultron, which Jarvis turns against everyone and becomes evil (perhaps the government gave Jarvis more intelligence and a mind of its own in an attempt to create a new Iron Man which Tony Stark destroyed in Iron Man 3).
Therefore, the Avengers Assemble again, and Tony Stark creates the Stealth suit (referenced in Iron Man 3) which is Black and Gold, and because Tony Stark had surgery, the suit uses more power now that it doesn't act as a life support machine.
I may be completely wrong, but that would explain all of the loose ends.