I would try to stop the dummy in the day to start with. does he have it other than to sleep? When I stopped Alex's dummy I did it firstly in the daytime and did sh-pat, when she was less dependant on it during the day (it took 3 days) i decided that she would be able to sleep without it during the night as well, it took 2 further nights and that was that. She was 9 months old.
I really think that if you ditch the dummy you could work better on the nightwakings as at the moment he is waking and he needs it to fall back to sleep, he doesn't need it to sleep, but he needs it to settle. We all wake, babies, children and adults, but we can usually put ourselves back to sleep, but if we have props to fall asleep initially then we will need it again when we wake during the night. (am I waffling again??? sorry!)
I also think that you should start working on an earlier bedtime if you are starting the reduce the morning nap as he will need to go much earlier than 7.45 when he is on 1 nap.