Well, let's see: Yes, 2 to 3, about 7, it depends!
Yes, EVERYONE, including children, can and do play. Every seat has a keypad, so you are playing against possibly 600+ other people at any given time. They usually start each show a fastest finger question, which everyone can answer, so speed is very important. If you don't know the answer, it is best to guess a combination of letters quickly. We've seen many kids get into the hotseat by guessing. After the initial question, the next contestant is determined by checking the audience scores, which is a combination of your correct answers and how quickly you answer the questions while the hotseat contestant is playing.
The shows generally last about 35-40 minutes, so depending on how far the contestant goes, and how slow the host is, they usually get at least 2 people in the hotseat, and sometimes as many as 4, if there are some early exits.
There are about six to eight shows every day, depending on the park hours. The first show is usually not until around 11 am.
The questions start out easy, then turn moderate, and then become much harder. You have a time limit of 15 seconds for the first 5 questions, 30 sec. for the second 5, 45 seconds for the next 4 questions, and I believe 60 sec. for the last question. The biggest difference between being in the hotseat and playing in the audience, is the music, and lights, and that infernal clock ticking down while you're racking your brain for an answer! It's exciting!
But be warned, it's addicitive!