Thats fair about the pacing. I thought the change in clothing/ facial hair/ magic capabilities showed time going by but maybe thats just me. Plus there's his memory and the fact that he seems to just have natural talent as Wong and Mordo commented.
I completely disagree about him going from zero to hero. There was a journey before he decided to want to help to save the world. He commented numerous times on his hands slowing him down or being frustrated that they weren't fixed yet. When he first used the eye of Agamotto and Wong told him about Kaecilius he said he wanted nothing to do with it, he just wanted to fix his hands. Everything he did during the fight scene in NY was in self defense, not to save the world. When the Ancient one tried to give him the title of master he rejected it, clinging to being a doctor and fixing his hands. Then when the Ancient one was dying and they were having their little astrial chat she told him the most important lesson he had to learn: It wasn't all about him. Then after she passed he talked with Christine, who in the beginning of the movie told him that he could save people in a different way, and he brought up that original conversation they had. Thats when you see the shift in him and he becomes sorcerer instead of a doctor.
As far as not saving the Ancient one I believe there are two reasons for this. 1.) Wong and Mordo told him he was not to tamper with natural laws, going back and saving her would be doing that. Now I know he ignores that at the end when he turns back time to save Hong Kong but he only did so after the Ancient one told him that sometimes rules needed to be broken. 2.) The Ancient One said that she had spent decades peering through time and every possible future ended right at that moment. So I took that as no matter what Strange tried, she would die.
I do think that Dr. Strange and Tony have similar personalities but it didn't bother me. In fact it made me excited to see those two characters interact on screen together.
Agreed again on the villain. I enjoyed him though. Especially that whole Mr. Doctor exchange