If you are talking about January 2015, you better find out immediately what is available and book what, if anything, is available. Usually resort decorations come down between the third and fourth or fourth and fifth of Jan (they are taken down overnight). Park decorations last a little longer and lately have been defined by the last night for Osbourne Lights at Studios, which runs until Jan 5 2015 and thus they will start taking park decorations down after the parks close Jan 5 and those take a few days before they disappear entirely.
As to crowds, since Jan 1, 2015, is Thursday, you will have Christmas like crowds until Sunday, Jan 4, when they will start to decrease and will become more January like by Tuesday. The marathon "weekend" then begins on Wednesday, Jan 7, and park crowds will be somewhat larger that Friday and Sat but still manageable.