Also poke through the parent website (links at top of page) for all sorts of great info.
The basics are this:
Overall budget you have in mind.
How will you get there? plane, train, auto, bus
Which resort, onsite or offsite?
How long you want to stay - and how that changes budget.
Park tickets - you probaly only need the basic version for your first time
Getting a schedule of park hours
knowing when you plan to go - and how that changes budget and crowd levels (any time kids are out fo school is going to basically cost more and be more crowded, usually dramatic difference)
weather averages for when you want to go - summer is hot, winter/early spring is cool/cold/warm, summer/fall are rainy/hurrincaney/thunderstormy.
Where you want to eat - both in general sense of Quick serve vs. table serve and amore specific list of places you'd like to try out - IF you want any table serve places, you'll pretty much need reservations in advance.
Know in advance WDW is a big place with lots of choices. You probably won't be able to ride every attraction and see every show because there is so much going on all day and night. but being inthe heart of teh fun is part ofthe fun!
Tweaking your dates by a few days can often give substantial savings.
Another sight which gives organized answers to many of your overall questions is allearsnet.com.
My other universal advice is: try to get in shape by walking before you go, amke sure each person has at lesat two pairs of good walking shoes- and perferably at least one pair of shoes that can get wet for the water rides and rainy days(Flip flops or
Crocs) They can also be very useful at teh pools. My preference is one pair of sneakers (socks) and one pair of high quality walking sandals (no socks). Your feet/legs are your most important asset at WDW! (after your wallet, that is!

)