Plan on six months or so for your first trip. Then you will know what you want to see when you return in a few more months.
Seriously you have a lot of planning to do. Get the Disney trip planning DVD. How many are coming? How will you travel? How will you camp? What will you bring? How long can you stay? What do you want to see or do for age appropriate activities? What is your budget? How much will you go over-budget?
Give some hints about your party and you will see a wealth of information from the fiends...some good, some bad, some in jest. Enjoy the planning as much as the trip.