The NCL cruise directors have always told us there is no required tipping...all the staff have been accomidated, unless you get exceptional service where you feel a tip is in order.
We've never booked a suite. I can tell you though on our 8day cruise we tipped our stewart $50. for the kids crew we tipped at the end I think $50. The girl said it gets divided among them. We kind of wished we tipped the girls individually. You can do which ever.
Also on the jewel my husband and I only tipped the waitstaff in the pay restraunts. But this last cruise on the sun with my friends, the waiters in the main nonpay restraunts were so go that we slipped them a cash tip at the end of each meal. They really were greatful!