Our flight was in at the airport at 10:30 - got to the dock about 11:30 and was on the boat by 12:30. Not sure how early they start, but like most ships, not access to your cabin until 1 or so. As for documents, Passports and the stuff in the cruise packet you got. THere are also some forms you print off online that can be filled out ahead of time.. To be honest, my wife took care of all of this. But the more you have filled out, the better. There is also a place to register your kids for their program groups. I would highly suggest doing this at the dock instead of on the ship. The line is shorter and moves quickly. Also the last thing you want to do is to have to wait in a line once on the ship with a kid that wants to go play in his area. Our kids where 8 & 10 so we gave them checkin and checkout priviledges - that worked great. Our 10 year old stayed out to midnight a couple of times and it was great to not have to stay up. They both knew they had to be back in the cabin at 5:30 to get ready for dinner other than that, we never saw them much.
Boarding was very well organized and with so many flights coming in, the times people arriving at dockside was spread out nicely.
The dockside area also had a band playing, a character photo-op and some several TV's playing old disney cartoons to keep the kids busy while you are checking in.
All I can say is rest up - there is way to much stuff to do with the childern programming, the family and adult activities. Then add in the character appearances - I could really use a 30 hour day. No time for napping on this cruise. I also saw one child that wanted to go back to the their program instead of having Ice Cream - that says a lot about the quaility of the programming.