As DisneyJamieCA mentioned, almost all of the parties sold out last year (2013). While no one knows if that will be the case this year, I'm guessing that they will again. My guess is that they aren't going to sell super quick, but they will start selling out in early September. The first ones to sell out will the Halloween night party, the first party, and the 10/2 party (Friday of Gay Days weekend). So if you were planning on going to one of those parties, I would probably buy my tickets in August.
Otherwise, Haunted Mansion Holiday and Space Mountain Ghost Galaxy will be up and running during the day. Big Thunder Ranch Carnival/Jamboree will also be running during the day.