I'll answer them one by one, but also see the next thread about the Norway...
1. Do you have to pay extra to dine in the " Le Bistro" and, if so, how much?
Yes, LeBistro is $15 pp.
2. I heard all rooms were non-smoking rooms. Is that true?
Not exactly. Smoking is permitted in cabins. There is no hard and fast rule here. If you don't smoke, don't smoke. If you do, be polite.
3. Last cruise was RCL and the kids used a credit card offered by that line. Does this line offer same? Yes, NCL does offer a credit card. Details can be found on their website: www.ncl.com
4. Is there a buffet lunch or only sit down?
Both. Open seating for lunch and breakfast in Leeward. Buffet at breakfast and lunch and dinner in the Great Outdoor Restaurant.
5. While in St. Thomas how much is a car rental?
It's not alot but are you sure you want to do this? Driving in St. Thomas is on the left, as it would be in England, Ireland, etc. Hairpin turns on the left get's pretty hairy. Think twice about this, but to answer your question, car rentals vary depending on the type of car: 30-100+ per day plus insurance...and don't even think about doing it without the additional CDW.
6. At the bars, do I have to pay cash or can I charge to mu room?
All purchases are charged to your onboard account. You will sign for these as they occur and pay for them at the end of your cruise.
7. Is there a charge for food brought by room service?
No, but it would be nice if you tipped a few bucks. Those people work so da## hard!
For more info, here's a few websites:
(This last link is a German site with some English pages available...EXCELLENT WEBSITE!)