1. There isn't a specific job to build a casino, however I see a lot of people switch to Hotel Owner.
2. Weird one. If you haven't outlined any rules, then really the players shouldn't gamble as your game hasn't been set up. If they give you their money when you haven't outlined the rules of the gambling game you're hosting it's kinda their own fault.
3. I don't think you understand the math behind probability. If I have to roll 10, but also get 10 to win, I have a (1/10) * 100 = 10% chance of winning. However, if I have to roll 100 and get 100 to win, I have a (1/100) * 100 = 1% chance to win. So yes, that would be scamming. You aren't following the rules you've outlined to your game and you are also attempting to deceive players through misleading probability maths.