For a first time cruiser, the dining package is not worth it. You're better off picking a night or two and picking a specialty restaurant as one-offs, and not with a package.
If your upcoming cruise is a 5 night sailing and that ship alternates 4 and 5 night sailings, if you check the menu while that ship is on a 4-night cruise, you'll only see 4 nights of menus.
Also I'm on Mariner in December. That ship currently is on night 4, which of course today is Thanksgiving, which has a special menu. The menu right now for my cruise on night 4 doesn't appear
Exactly. They're splitting it up with communities. If you don't want the family/kid side of it, there's plenty of space to be just an adult. Unlike other ships where it blends together.