I am no scientist - clearly - but I always assumed 223 was in the same system as 426.
Why they didn't terraform 223 is a good question, but maybe the intervening events of Prometheus (the death of all hands, including Weyland and daughter, and whatever scant information returns to Earth) and/or subsequent sequels could explain it. Or maybe they did and we just don't know it.
As for the Engineer, I inferred from the film that his mission had been to head to Earth and cleanse the planet and that, yes, he was outraged by the evolution of a species which, I suspected, was never intended to get that far before being harvested. When he saw humans had infiltrated his installation, he was infuriated; he attacks them, then gets ready to head off and complete the mission. As Scott said about the derelict in Alien over the course of so many interviews and commentaries over the years, the juggernaut is a bomber and the Engineer/jockey its pilot.