Hi and welcome!
You're right, it is big, but don't let that intimidate you.
Assuming you haven't made any big decisions yet, start with the resorts board. First, take a look at the resort options at
www.allears.net -- they have slide shows and fact sheets on each of the resorts. Once you narrow down your choices, the resorts board here has a series of threads on each of the resorts. You can find things like which location you'll want to request.
Your next decision is whether or not you want the meal plan. We love it, but a lot of people don't. Take a look at the dining forums to narrow down where you want to eat-- if you have kids, you'll want to look at character meals. (Take a look at the princess meals at Aukerhaus in Epcot, and at dinner with Cinderella and friends at 1900 Park Fare for your "4 little princesses."
Oh, and on the family board, register for a "fairy godmailer." Someone who is going before you do will send your kids a postcard, anticipating your arrival. When your trip gets closer, you sign on to do the same for someone else.