1. No. You may run a class with one student.
2. Given the significant hands on component, I prefer to limit the upper number of students to 4 or 5 absolute max to ensure a quality learning, assessment, and feedback experience for each student. As far as an optimum certain number of students, it is highly variable. I think it is up to the Instructor to dynamically create optimum learning, assessment, and feedback experiences for each individual student as well as the class as a whole, regardless of either the class size or the relative knowledge/experience levels of the students in the class.
3. What are your thoughts?
I have done classes with 1 person, but do not recommend it on a regular basis. NRP is a team sport-therefore you need a team to accurately simulate a resuscitation. 3-4 people is best, but I will do up to 8 and have 2 teams. One watches while the other simulates.