Hi Finbob,
I am not an instructor, so I am just giving you my experience as a student...
Q1: The course covered a whole range of skills--self-rescue, a variety of rescue scenarios, applying first aid to rescues, managing rescue scenes. I think browsing the manual would give you the best sense of what is covered.
Q2: It seemed that PADI Rescue basically picked up where the Advanced Open Water course ended. People in my class who had AOW skills, including very good buoyancy control, seemed to do well in Rescue. There were 1 or 2 people in my class who lacked basic skills (no buoyancy control, couldn't assemble their gear, etcetera)--they struggled and basically could not learn the rescue skills. Also, people got out of it what they put into it--those who studied the readings, showed up for every class, and practiced the skills until they got them right seemed to do well.
Q3: I didn't find the course very tough physically. I think that if you are physically active, the course is very doable. The course includes techniques that help with the physically demanding aspects of rescue like lifting victims on to a dock. Having said that, I have heard a lot of people say that they were wiped at the end of their rescue scenario day.
Overall, a fantastic course--really useful, interesting, and even fun at times. I woudl really recommend it.