The casino missions are pretty easy, and you probably won't lose much money if you have a decent strategy. You can for instance google 'craps safe bets' and read some quick guides if you have no idea how to play that game.
yes bet 1 million, I got lucky on the keno won 50 million, after I had spent 20 million trying to get 10 million in the other ones. High and Low I go for 3 rounds and collect, its the only hard game to get 10 million in that is betting 1 million. 100k will take time.
Each mission differs in money and games mine had 10 million in each game.