Balcony rooms are the best! You can't go wrong with a balcony cabin, regardless of location. I have never been on the Gem but I have been on the Jewel, Dawn, and Star. The Jewel is similar to the Gem from what I understand.
DINING: Every time I have cruised we have eaten at the buffet for breakfast and lunch (or the pool side buffet). Breakfast and lunch are also available in at least one of the main dining rooms and I would suggest doing that for a more laid back dining experience. Your Freestyle Daily (a little newsletter you get in your cabin every evening for the next day) will have details on what restaurants are open and when. We ate a combination of main dining rooms (complimentary) and specialty dining rooms (fees ranging from $15 to $35 per person). The main dining rooms are good but the specialty dining is great. Definitely try the Italian specialty restaurant one night ($15 per person) where you can get a variety of great food. They have great fish, steak, and various Italian staples. I have dined at the Italian restaurant twice on each of my three cruises, so 6 times (maybe even 7)! The specialty dining room fees cover anything you want to order on the menu, with the occasional rare exception that is very well noted on the menu. Alcohol and soda/pop/tonic are not included in any of these options, but coffee, tea, and water are included. Juice and milk may be available for the kids, but I do not know for sure. Juice and milk are definitely available at the buffet and are complimentary.
FREESTYLE DAILY: This little newsletter is your key to everything going on onboard, including dining (as mentioned), activities, shows, and the schedule for days in port. I usually carry it around with me each day. Extra copies are available at the Guest Services desk if each member of your party wants to have their own.
ACTIVITIES: There are plenty of things to do onboard. Some are free and some have a fee. Wine tastings, pub crawls, and Bingo are some activities that have fees (makes sense right?). Some free activities include shuffleboard, large chess/checkers, the fitness center, arts and crafts, and karaoke.
PORTS: I have been to Cozumel, Costa Maya, Roatan, Belize City, Nassau, Great Stirrup Cay, Port Canaveral, and Bermuda. I have written reviews on all of these cruises which you should be able to find via my profile. Any questions, feel free to ask!