I don't have the family you do, but I grew up in Orlando, and my mother worked at Disney for years. So I can at least give you my two cents on the Disney vacation. First of all, I definitely recommend staying at a resort. Orlando is not very public-transportation friendly, and you will need to rent a car, and paying for parking back and forth to the parks each day will eat up the difference between what you may save staying off-property. Staying on property REALLY gives you an opportunity to enjoy your stay, and get the most out of the parks. You can go back to your hotel for meals in your room (this will save you a TON of money), and you won't feel rushed to get through each park during the day. Take a break after lunch to swim & relax by the pool at your hotel, as the busiest time in the park (read as: most miserable) is about 2-5. Go back after dinner and you'll really enjoy a nice evening there. Also, when you stay at a Disney Resort you will get a card that will allow you to skip the lines at many rides -- WELL worth it.
A couple of money-saving tips: buy your souvenirs OUTSIDE the park, on International Drive (near Sea World) to save the Disney mark-up. Like I mentioned before, buy some groceries once you get there, to keep in your room for meals like lunch and breakfast, and your own snacks, which will also save you a ton. Buy some bottled water as well, to cart around yourself. All of the food there has a ridiculous mark-up, and the more you can cut out, the better off you are.
There are Disney Vacation consultants you can call at Disney, to help you plan your vacation, but I agree with the PPs who have recommended AAA, as they will be able to give you non-Disney advice and coupons as well.
Most of all, enjoy yourself! I have probably been to Disney 1000 times, and I still love it as much as the first time! It's a truly magical place, and I hope your family has a magical vacation!!