I change after takeoff in case of a change of plans... You can change into the PJ's in the oversize lav on the left. There is a drop down pad to prevent stepping on the lav floor with your dirty shoes or slippers (provided).

There will be PLENTY of food starting 1 hour after departure.

There are no beer kegs!

YMMV but as a westerner, consider my wife's experience with the Japanese meal; avoid it. She ignored my advise.

There is a great snack menu for you to enjoy any time. Enjoy! I also add ice cream to my snack mid-flight. (usually the burger and ice cream)

Enjoy! The NH experience is very good!