Coinflip is a thing by the way. Coinflip is basically a roulette wheel (colour not number). You can't really gamble crate keys, since you can't withdraw them like you could do with something like.... wardrobe. Player run casinos in the past have worked out really well, myself having owning one of them.
But from my experience owning a casino (player run), the people who gamble often want refunds, or get mad because they don't win, or think the games are rigged. Some players will of course win money over lose, but the mast majority of players will lose. The redstone itself is also a pain to do, as chunks only have a observer limit which can handicap the redstone machines you would like to make.