For your park tickets, I would say that you need 5 or 6 days. It all depends on how you work your trip. We never go to a park the day we get there, usually its too late. Instead we just check out the resort, and have dinner. We always have a 'day off' - no parks in the middle of our trip. We have little kids too, and really need a day 'off'. We go swimming, and explore DTD. And this trip we do not plan on parks on our departure day either. So for our trip Sept 19-27th (8 nights) We will have 6 day tickets.
As for the dining plan you with have six counter service, table service, and snack credits each. You get a credit for every night that you are there. You can easily stretch your dining plan to cover 7 days though. You can not choose how many days you have the dining plan. It is for how many nights your stay is. I hope that is not confusing for you???
Another thing to keep in mind is that you are going when is is going to be busy for the christmas season so make sure that you make all your table service dining reservation as soon as you can. So you get the times and restaurants you want.
Like I said it depends on how you want to do your trip.... And your it depends on your kids.
We know we will be back so we try not to have the 'must do everything' attitude. We did this on our first short trip to the world, and it was not so fun
I hope that helps, and I hope that you guys have a great time.
