Welcome! Another MA resident here.
A couple of other options for rooms that will fit 5 are the Cabins at Fort Wilderness, and renting points for a 1 bedroom DVC villa. Both of those would give you the option of a full kitchen, if you wanted to make some meals in the room to save $. But AoA does have a great food court!
This year, there is a room only discount for spring, up to 30%, so make sure you look at the special offers when it is time for you to book. You can either then add your park tickets through WDW or there are a couple of places that offer a little bit of a discount if you want to get them separately.
I think you're right in not getting the park hoppers with 5 year olds, unless you don't mind spending the extra $. You can always leave the park to go back to your resort midday, then just return to the same park that evening. It just takes a little bit more planning to know which parks you want to do on which days.
Also, not sure if you're thinking of adding it, but personally, I would not get the dining plan, especially the quick service one. I think you can do better on your own, cost-wise.
As far as airfare, we had great luck with AirTran out of Boston last year, and Southwest for this summer, out of Providence. I always check right when airfare is released on each site. I love Jet Blue, but we never seem to get lucky and get the lowest rate with them.
If you do book a package with Disney, another way to save a little is to get a Disney Visa card. I believe you get 6 months 0% financing when you book a room and tickets together. And, with the $ you spend you get points for reward dollars you can then use at the parks.
You probably know, but if there are places you are sure you want to eat, like a character meal, just make sure you book those at 180 days before your trip.
So many options, have a great time planning!!!
If you have any questions, feel free to ask!