Read
this for a really good description of the party.
The cookies and hot choc are unlimited and set up in a few places.
They will let you in after 4:00p with just your party tickets and they will set up a separate entrance for party goers and give you a wristband to identify you from the regular guests.
Once 6:00p comes around you will be herded to either Fantasyland or Tomorrowland until 7:00p. That way they can empty out the park. If you are eating in one of the restaurants, then you will not be herded unless you finish your meal early....but if you finish by around 6:30 - 6:40 then you will just wait in front of the restaurant till 7:00p.
There are a few special Xmas shows only seen at
MVMCP (and the week of Christmas) see my link for them.
Hope this helps!