I hope you have you ADRs made. You get a lot of meals with the deluxe plan.
Flying with kids is mainly setting expectations and providing diversions. Explain to your kids what is going to happen. Have games, videos, books, etc to keep them occupied while waiting at the airport and while en route.
Clothes - we usually drive so I pack heavy. We also usually travel for 11 days. Still we pack a few changes of clothes and do laundry one day in the middle of the trip. Personally, I like to change clothes when we take our midday break. It helps me feel refreshed. Since it is hot during this period, I can fit my clothes in a suitcase that fits in the overhead. (I have a no long pants or socks rule for myself on our Disney/beach trips.)
There is enough to do to keep you busy for nine days. You may want to consider a water park day. There are areas in both Typhoon Lagoon and Blizzard Beach that cater to smaller ones. My kids love the water parks. If you want one day it is slightly cheaper to buy a separate entry. There is an option for a little more that matches the number of ticket days. There are a couple of well themed miniature golf courses that you would probably enjoy. And frankly, the deluxe dining plan will give you a lot of break time.
Here are a couple of threads on packing advice. I can't say that we do anything unusual. We usually take a couple of trips a year and it seems so rote I would forget items.
http://www.disboards.com/showthread.php?t=1884129&highlight=packing+lists
http://www.disboards.com/showthread.php?t=2690044&highlight=packing+lists