Yes, I agree 100% with Kevin....if you can rent a car DO IT. It will make life MUCH easier. You can be at the parks at opening and knock out a lot of big rides before the crowds arrive around 10-11am. You will need stamina to stay at a park all day from opening to closing fireworks. Without a car, its impossible to return to an offsite hotel during the day. This makes for very long, tiring days and by day 6 you will be burnt out!
Try to arrange quieter days in between busy days, so if you plan a full day at Magic Kingdom, then make the next day a water park or shopping day. Be flexible with your plans...by all means have an idea of what you want to do each day, but dont worry if you stray from it...the idea is to have fun!! I usually have "back up" plans in case no one fancies whats on offer that day!
Bear in mind, for the first few days you will be up very early, so try to plan early starts at the big parks then. Save the later attractions like Fantasmic, Illuminations and Spectromagic until later in your holiday when you are adjusted to the time more.
Its difficult to plan an itinerary for someone you dont know, as everyone has different priorities...if you are Coaster fans then you will not want much time at Magic Kingdom, but may want a couple of days at Islands Of Adventure. If you are animal lovers, then you may want 2 days at Sea World. If this isnt appealing to you, then only one may suffice. You need to sit down with your family and decide which parks you think will need more days (this may change when you arrive of course!).
Also, face up to the fact that you wont be able to do everything in one trip!!! Make your list of "must dos" and then "would like to do". That way you wont miss out on the attractions that appeal to you the most by being diverted by things that are of less interest.
Keep at least 2 days "free" in your itinerary so you can return to a park that you enjoyed the most or didnt get to see all of.
Happy planning!
Allie