I think it is hard to get caught up in a lot of must do's especially when hearing from those of us who have had occasion to cruise Celebrity on multiple occasions.
My main advice is to (REF) Relax, Explore and have Fun!!! Reflection is a favorite ship of ours mainly because of the multitude of options available to passengers. For dinner you can dine casually at the Oceanview cafe, have a served meal in the dining room, or enjoy a dinner at 6 specialty restaurants. If you are in a suite you can also add Luminae and Blu to your dining options.
There are multiple bars all over the ship, each with it's own vibe and potential for live entertainment. There is a wonderful coffee/pastry bar. The casino is one of the nicest at sea. We are not spa people, but always hear good things!!
Wishing you a wonderful cruise!