1: 2x blackjack, 2x poker, 2x roulette. Will check minimums.
2: Twice a day. Not sure what you mean by how many stewards. We’ve only ever had a single steward. I'm sure if they were unavailable for some reason someone else would cover but in 30+ years of Cunard cruising I've never known that to happen.
3: Yes
4: Depends on your check-in time and cabin grade. Probably Lido/buffet or Golden Lion.