You can do The Doomsday Heist or The Diamond Casino Heist. Both require 2-4 people. For the older heists you need 4 people total and the Cayo heist is unplayable unless you're doing it solo.

The Diamond Casino Heist payout is by far the highest in GTA Online. The rewards for the mission add up toR$10.34 million on normal difficulty, and it can go up toR$11.37 million, if the heist is on hard difficulty.

If a casino patron wins an unusually large amount of money, the casino may take certain steps to manage the situation. This could include closely monitoring the player's activities, reviewing the game's integrity, and potentially limiting the player's future access to certain games or the casino itself.

No, but there's no reason they would ever kick anyone out for that. Far more likely, the player would get a comp of some kind to encourage them to play longer.