Before I answer your questions, lets be clear that this is a comic book movie. If your enjoyment requires not suspending belief and plots that hold up to rigorous scrutiny, you're not prepared for the genre.
But as it turns out your scrutiny wasn't rigorous. Strange didn't make a prophecy. He looked at 14 million of infinite possible futures. He found 1 where the good guys win but that doesn't mean there aren't others. He also didn't take the time to scope out these futures until they were already waiting around to spring their trap on Thanos so this is a bit late to hide Tony Stark. It also doesn't mean Strange knew their trap wouldn't work, which it almost did. And yes Chis Pratt romanced the dog pretty hard.