I would not have breakfast on an EMH-morning. The park gets so crowded on EMH mornings that it's not good to spend your time in a restaurant as more and more people enter the park.
However, if I HAD to decide (if this was the ONLY day I could possibly go), I would go at 9:30 AM, and arrive at the park before the EMH begins, so that I could take advantage of that first hour. You could get a lot done in the first hour...we did all of Fantasyland by 8:20AM last summer! Of course, this is provided that you are staying on property and can get into the park for EMH. I would definitely not go at 8:05 on an EMH morning. So maybe try it that way...I know how important it is to eat in the castle as it is such a unique experience.
Another option is to have lunch at the castle...you could get everything done in the morning when the park is less crowded and then have an early lunch when the park gets more crowded, if the ADR is available.