Any ways to improve my book idea?

Here's a quick idea of what I'm writing: 100 people have signed up for a contest that they know nothing about. All they know is that one of them is leaving with $500k. The contest has five rounds: a game of would you rather (like the movie), dares that vary from a mild slap to torture, anonymously voting people to die, anonymous would you rather, and the last two contestants fighting to the death. I've planned for the book to begin at the start of the game with the characters being referred to by their numbers (so the auduence feels like they've never met these characters before just like each character will). They all have different personalities as well. The characters will slowly fall into madness to be the last one alive. There is no main character (this is to avoid plot armor and to not have it focus on one single person), and the audience will be guessing who will die and how they'll die. I want to know if there is any way I can improve this idea in any way.