1) There is a charge for ANY Internet use on board the ship, unless you have some way of connecting with a satellite yourself (some people do have this ability). It does not matter if it is wireless, cable, your computer or the ship's computer. The cost is the same regardless.
That said, when I was on the NCL Star (a sister ship) I was in a normal balcony cabin, but I did not use the Internet. When I was on the NCL Jade (another sister ship) I did use a cable to connect to the Internet in my cabin. However, I was in a suite. I don't know if the normal cabins have that option.
2) Yes, you can see it in the photo below (this is from the Star) ...
3) No. It is considered a fire hazard. No cruise line will allow you to have an iron in your cabin.
4) No, the ship will hold your purchase until the last night. That applies to bottles you buy on board also.
5) You have to pay extra for bottled water also. However, the tap water is filtered and is very good. Just add ice (which is also free).
6) The biggest difference between NCL and other lines is Freestyle Dining. Learn which restaurants are free (included) and which cost extra. There should be at least four free restaurants:
...The two main restaurants.
...The buffet.
...What I call sit down fast food. I am not sure what it is called on the Jewel, but it serves the hamburgers, hot dogs, fries ...
If you want to eat in the main restaurants, learn when they are least crowded. Otherwise there may be a short wait. Just after the first show ends is one time when the restaurants get very crowded. Just wait about 15 - 20 minutes and the lines will go down. Also, there may be a time (usually very early or very late) when most of the extra cost restaurants are half price. It will be listed in the Freestyle Daily (the ship's newspaper which you will find on your bed every evening). On my second cruise I either ate for free or half price, except at Teppanyaki, which never reduced its price.
You can make reservations for the all of the restaurants except the four listed above. When you can make those reservations depends on your cabin category (the more you pay for your cabin the earlier you can make your reservation). The Italian restaurant was very popular on both of my cruises, but then it was also free. I believe they charge extra now. Teppanyaki is also very popular. I don't believe you will have a problem making reservations at any of the other restaurants. You don't have to make reservations. I was a walk up several times and was seated right-a-way (your experience may vary). Reservations at Teppanyaki is a must.
Learn to "work the system" to your advantage (as I did) and you will have a much more enjoyable dining experience.