Did you miss theteaser trailerthat Marvel put out for Avengers: Age of Ultron? It shows the Iron Man helmet being transformed into Ultron. Not to say that Tony Stark is responsible, it's just that it looks that Ultron's body will be fashioned from an Iron Man suit.2) We don't know that Ultron is coming from Stark. Please link proof ( all Ive seen is tons of websites speculating, link me the official statement from Joss himself)
The rumor going around is that Stark will make some changes to Jarvis (probably at the behest of SHIELD after the events in Iron Man 3), and it all goes wrong.
Not really. I've read speculation that the Chitauri were dead Skrulls that were reanimated and enslaved by Thanos, so blowing up that big mothership took away Thanos' control over his slaves, and they went back to being dead.1) I agree, there are plot holes and bad devices in pretty much every fantasy/action movie. The thing about most of the recent movies, including Avengers, are that the plot wholes are pretty fucking massive. I mean all the aliens just dying when their ship blows up and even though mind controlled Erik Selvig builds a back door to the tesseract? Just a few of the things that make you go WTF.
Dr. Selvig was working for Loki. Do you honestly think Loki would trust that Thanos' army would pour through the portal to Earth, take the tesseract and leave Earth for Loki to rule? That's why Selvig put the back door into the portal generator. It required the staff that Loki had in order to turn it off, that way if the Chitauri came through and Thanos decided to change their agreement, Loki could shut down the portal himself.