I understand the nervousness. The first trip I planned for the kids, I was a nervous wreck until it was over. I wanted everything to be perfect. I was hoping I was making the right decisions that would be just what my kids wanted. It was not a perfect trip (chafing, oh my goodness, the chafing! and the Disney rash). However, it was so much fun and so many great memories and some of those plans I had made, we cancelled. Your kids will have a blast. Were there disappointments? Yes. You can't control everything, such as the kids standing in line for 25 minutes to see a character and they are next up and it starts raining and the character leaves. It happens and the kids cry. Or, the pin backs that you bought that are supposed to keep those pins on permanently, don't work, and they lose their most favorite pin in the world. It happens. Or, the Mickey Sorcerer hat that your daughter buys, falls off her head during a ride and you end up having to go to the Central lost and found (kind of a dump and not very magical at all) and when it is returned it has black grease all over it. Or, you bought tickets for the dessert party and fireworks, and your youngest gets sick and you spend the entire time in the crowded yucky bathroom. We have had numerous things go wrong, but with all of that, it is still the most favorite place that my kids and I want to go.
So don't be so nervous you can't enjoy the process. They won't want to do things that you think would be perfect, before park opening character breakfasts for one. I am still bummed about not going to Crystal Palace before park opening, but they were very much against it. Plan what you think will be great. That is all anyone can do. They will think it is amazing.