It is overwhelming, but you'll have a good time no matter what you do. I've heard(gasp!) that there's some that don't plan anything at all and still have a good time
I guess the best tip I can give with regards to planning is deciding what parks you'd like to do on what days. Unofficial Guide Book carries per day historical attendance guides, although with the new MYM tickets, I believe they've done some updates on their website. Once you know which parks on what days, you'll have a better idea of what lunch or dinner PS's you'd like to make. IMO, as long as you have an idea what parks you're going to on which day you at least have a plan. And if you have hopper tixs and the park you're at gets too busy ,you can always go somewhere else. I would plan for an hour travelling time on the buses.
The only other tip-if you're travelling with little ones, be prepared for the unexpected, try to go along with the flow, and head straight for Fantasyland in MK first thing when the park opens. Oh, and another one that works good for us at any park, go straight through to the back of the park and work your way foward-at least if you arrive in the morning.
Have a great time, and read these boards for lots of good tips!!!