As Shoreguy mentioned, the ship will be filled with kids, maybe not 900 but at least 3 or 400, probably more; be prepared!!!
NCL is very gay friendly so you will have no trouble meeting other men and women. Yes, FOD will help.
As for other info, I haven't been on the Gem, not many have yet, but I think you will find NCL a great ship with lots of different type of people from all walks of life and all parts of the country. the night life is enough to keep most people busy but it isn't a big party ship where you will find the bars hopping at 4am. This is good not bad.
Do try at least one sur charge restaurant, it is worth the extra few dollars.
If you have anymore questions just ask. We are all here to help.