jtjarvis -
Just wanted to add that this would be my advice, based on what we did last year -
I would get to the MK around 4:30 and ride some of the rides - I would also, in conjunction with buying my tickets to MNSSHP book a PS at LTT where the characters and wait staff are in costume and or have face makeup, etc... It really adds to the evening to do this, and it gets dinner out of the way - make your PS for an earlier time - and if possible NO LATER than 6:00, because when the party starts at 7:00 you want to be through with dinner and ready to do the party.
If your kids are not big trick-or-treaters, this is where you will "waste" the most time - so skip it unless the lines are short and instead, spend your time soaking in the atmosphere and doing the "special" things like the parade, etc...
I would also advise being in Liberty Square for the parade to see the headless horseman and to hear the Tale of Ichabod Crane.
Hope this helps!