1. I used to be certified in CPR, but have not renewed for some time. I do believe it is a good idea for black belts and instructors. As for what the Sempai was doing, I have not a clue. You'd have to ask him. 2. Being overweight is a problem, and it has been discussed here before. Hopefully it is something that the student is working on, and wants to improve, and that is why he is there. Unfortunately, the only way the instructor can control it is by what he does in class; he could restrict his progress as motivation for losing weight, but that is about it. 3. Doing knuckle push-ups should not cause any problems. However, if you work with your hands, and are concerned about damaging or not being able to use them because they are sore, you may want to address this concern to your instructor.