Typical SOP:
Boarding is usually at least 4 hours before departure. You may not be able to get to your room immediately but the dining room is uaually open with a buffet. There's no customs since you're staying in the USA the whole time. The cruise lines are very organised and you'll be amazed at how quick & organised they are. You'll get tags for you baggage before the trip which you'll just drop off at the dock and they'll magically appear in your room. Take a carryon bag for anything you may need until you get to your room and valuables.
I always doubtful about trusting someone else but it works. Similar procedure on depaeture. You just put your bags out side tour door and the a ppear on the dock or bus on your departure.