24: You may fill in the hotel address too. But if you do not have that yet, you cannot apply for visa either (hotel reservation is one of the required documents anyway).

25: Same. I usually just fill in the hotel contact. Or you may fill in the organizer contact as well.

38: "Refused admission" is referring to 拒绝入境. I don't think you have that experience yet (and better not). Failure in visa application belongs to another entry in the form.