Looking for Answers about Norwegian Jade?

You may have to call NCL to get an official answer as I've not seen any references to using a VIsa prepaid card to settle onboard purchases. Refer to the following link for how to pay onboard expenses.

http://www.ncl.com/faq#onboard-expenses

NCL doesn't operate a shuttle but they can arrange for ground transportation from the airport.
http://www.ncl.com/freestyle-cruise/getting-to-the-pier

I don't believe you can send your luggage to the port without going to the port. Luggages will only be accepted at the time of check-in.

All ships have 110 V and 220 V A/C. The connector is US prongs for 110 V and European style prongs for the 220 V.
You may need an adaptor for the prongs if you don't use the US or European style prongs. High current appliances like hair curlers may need a converter to avoid tripping the fuse.
The outlets are limited and is not located next to your bed. You may want to take an extension cord if you want to connect some device next to your bed.

I don't believe that you will get a flatter pillow. You could call NCL's reservation desk and check with them if they can arrange one for your. Other option is to pack one in your luggage.

Yes. The spa onboard the ship has sauna and steam rooms.
There is an additional charge for using the spa services and facility. The ship will offer different kinds of packages for the spa. The packages vary ship to ship and by the ship's itinerary. Since the package details are not advertised on the website, the only way you can find out about the packages and cost is onboard the ship.

Coffee makers are only available in the balcony and higher class of stateroom. It's not available in the inside and ocean view staterooms.
You can order coffee through room service or pour yourself a cup of coffee at the Java cafe or the 24 hours Blue Lagoon restaurant.

Check out NCL's Facebook page or "Cruise Role Call" on other cruise related web sites for a possible answer. You can post your question there as well.

The shore excursions can be cheaper if you book them yourself or use a tour company at port but I prefer to use NCL's shore excursions even if the cost is a bit higher. NCL pre-screens the tour operators. Also, in case you are delayed in returning back to the ship, the ship will wait for you if you booked through NCL. If you made your own reservations, it is your responsibility to be back on the ship when the ship sails or risk being left behind.
Using an external tour operator is fine if you are planning a 3-4 hour shore excursion that leaves you plenty of time to get back to the ship.
Last year, we took NCL's shore excursion to Tulum in Cozumel. I believe it was a 7 hour excursion and we were delayed by 30 minutes returning to the ship. The ship departed after all of us were on board the ship. If it was something we had organized on our own we would have had to fly back from Mexico.

The butler's job is to take care of all of your needs and requests within your suite except for cleaning which is done by a cabin steward. The butler will help you unpack and pack your luggage, keep your suite stocked with beverages, deliver food and beverage orders, serve you breakfast, lunch & dinner if you prefer to have it in your room, etc.
The concierge will make specialty restaurant reservations, book shore excursions, provide reserved seating in the theater, and provide information of all onboard activities.