Hi Marie!
I am so excited about your upcoming visit to Walt Disney World. By late November or early December when you arrive, the Parks and Resorts will be decorated to the hilt in preparation for the holiday season. It is beautiful. You are going to love it!
Like you, I am always wondering which Parks and Resorts are the least crowded on certain days. Unfortunately, it is impossible to predict because there are so many variable factors that determine the numbers of Guests visiting at any time of year. I have found, however, that the crowds usually seem to increase during school holidays as well as times when special events are being held. One way to avoid the crowds, however, is to take advantage of
Extra Magic Hours which are offered to all Guests staying at Walt Disney World Resorts. Each day one park is either open early or stays open later than usual so Guests can enjoy the magic just a little longer. It is a great way to squeeze every bit of fun out of your time there. As far as your check in day goes, yes you are able to check in any day of the week you would like. There are no certain requirements for reservations to begin or end on any particular day.
I hope this helps. Please come back if there is anything else we can do for you. Have a wonderful day!
-Nancy-