Since you have Sunday set aside I would stick with that! I promise that if you get there early (on a Sunday that is 30 -45 minutes before park opening) you will get a lot done. Then when the crowds get really big maybe go to DTD, have lunch and shop. Or see the Aladdin show. Even though you may have to wait in a long line, waiting in a long line for a 45 minute show is better than waiting in a long line for a 2 minute ride. We always ride rides in the morning, have an early lunch, then see shows and by then its parade time. On a Sunday a lot of locals will leave after the parade. If you have a gameplan and utilize fastpass you will be just fine. Don't worry, you will have a great time!