Agree that you should buy as soon as the tickets are available. In terms of when to go. We have always opted to go on a weeknight. Not that there is less people on weeknights, it's just our preference to not go on a weekend night. You are going at a good time when most kids are still in school. We were at WDW last year from Nov 30 - Dec 11. We went to the party on a Tuesday, Dec 8 and was able to get on all the rides with no more than a 20 minute wait.