James - Re: "No more questions." The biggest benefit of this protocol is that it has students consider the phrasing/delivery of their question before asking. By nature of that, often times they are able to investigate the answer. The way this has most frequently played out in class is that a majority of groups are so concerned about conserving questions that they'll either use zero or only one question throughout the duration of the lesson. In rare situations where groups have used all of their questions, I will always offer to hear their questions but maybe only give a hint, respond with another question, or refuse to answer (if I believe it's within their abilities). I never want students to feel hopeless or give up.
The iteration process is definitely a balance. There is a sweet spot where most students are proud of their product. Any less time and students feel like it's "unfinished." Too much extra time and students get bored, frustrated, etc. At the actual carnival, most students exhibited their v2.0 or 3.0 design.