lux, welcome to the DIS.
You can go to this thread for helpful info like setting your coutdown counter!
http://www.disboards.com/showthread.php?t=439040
Here is my recommendation for your trip:
Schedule in am & pm time frames. Take a break in the afternoon for swimming or relaxing back at the hotel. Allow for park hopping if you so desire.
2 Full days (2 ams & 2 pms) at MK so you see the parades & fireworks. I relly hope you get in to CRT. If not, you can got to PSB in EPCOT which is great too!!
1 day at MGM
1 day at AK
2 Full days at EPCOT (WS a day & a half and FW one day). Don't go in to your trip thinking EPCOT will be boring for your kids. Start talking it up now. Be positive. Have your kids learn how to say hello, goodbye and thank you in each countries language (see thread at the top of this board). Buy a passport to get stamped. Make sure they do the kidcot stations (decorating a mask, getting a charm in each country). Watch the little shows, listen to the great music & try the new foods.
Keep a day open to go back and hit your favorites one more time, or go back & hit something you missed.
Other things to do:
Fort Wilderness, go in the evening & eat at Trails End buffet (cheapest buffet!) & then go on the hayride, campfire sing-along with Chip & Dale & watch a movie (see the camping board for the list of movies at the beginning of May).
Downtown Disney
If weather permits, maybe hit a water park
Also, I'm sure you girls will love pin trading. Our family got really in to it! We bought a bunch of cheap pins to trade for princess pins (dd is 4 & is very in to princesses). It was so fun! Other kids who did not have pins looked sad whenever dd was trading with the CM's. eBay has lots of pins for sale. They go for over $6 at the park but you can get them on eBay for around $3.
Have an awesome time! Bring lots of film!