Welcome to the DIS!!!!
To answer your question..... it just depends. Actually special events can work in your favor. For example, if there is a special event party at MK, it usually is NOT crowded in the park until 4 or 5 in the afternoon. It can be a great day to enjoy the park; but you will be kicked out before the fireworks and nighttime parades, so you would miss those. See most people with special event tickets won't go earlier because they'd have to pay extra, and people who aren't going won't go because the park is closing early. Now, people with park hoppers don't care about that so much, but you can tell the difference in attendance at the park. Also, the morning after the party can be a good time to visit the park as many people won't go there because they were there late last night. Kind of like hitting a park the morning after EMH.
Your biggest crowds may actually be at your resort. A lot of groups with young people will often stay at the Value resorts.
You'll be in Disney though, so just have fun.
