Carosello,
Welcome to the DIS. We went the last week of Sept this past year (Just after Hurricane Jeanne!) & here is what we did: (We had dh, dd1 & dd4)
Rented a 2bedroom/2bath villa at Wilderness Lodge (VWL) from Sun - Thurs (left on Fri) thru a DVC'er. It was $1500 for the room (out the door, no taxes of any sort). It sounds like a lot, but when you consider buying 2 value rooms & having to buy every breakfast & lunch it really is a great deal. The villas have a living room area, a kitchen & a w/d. We brought half as many clothes & did laundry half way thru! We grocery shopped the 1st day & bought food for every breakfast (except for our princess breakfast!) & every lunch (we came home around noon daily for lunch & naps for the baby/swimming for the 4yo). We also brought our own water into the park. It was great to buy fruit & snacks for the kids too. You could even eat dinner there too to save money but we were in the parks in the evenings. It was so nice to put the kids to bed & still be able to go into the living room to watch tv or hang out on the balcony (and drink our grocery store beer/wine!) or whatever! The resort you mentioned is not in WDW. WL is in the MK area & only a boat ride to MK which is ideal! The pool is great too, as is the whole hotel! Go to the DVC board if you are interested & see if you can get points from someone. What I actually did was go onto eBay & found someone "selling" a week at their DVC timeshare & then I emailed them to ask if they could get me what I needed (150 points) & they did & it worked out great! Dh & I had the "master bedroom" & my sis (who came to help out) had the other bedroom (2 beds) with my 4yo (each had their own bed) & hee hee, we put the baby (in a portable crib which is in the closet of your room, along with a high chair - gotta love it) in the closet which was pretty huge & fit the crib no problem!! So the family with the kids can stay in the room with 2 beds (3yo in one bed, mom & dad in the other) & put the baby in the closet!! The other couple can stay in the master.
For $1800 you could get a grand villa at OKW (near DTD) that sleeps 12 & everyone would have their own room (including kids). I don't know how many they have so you better get going to make sure any are still available! Go to the DVC thread for more info.
You have plenty of time to plan. Sept is very slow & very uncrowded (and still very hot!). It was great! We pretty much walked right on every ride. FP was not even working a lot of the time. 5 days is plenty of time. We split our days up into am & pm (with the nap/swim break in btwn which is why you want to be on site so you don't have to drive all the way back to a hotel in traffic). My recommendation for your aged kids is:
MK 1 1/2 - 2 days
AK 1/2 day am
MGM 1/2 day pm (arrive in time for afternoon parade & stay thru Fantasmic)
EPCOT 1 1/2 days (I was shocked how much my dd4 loved EPCOT, she really got in to making the masks at the WS countries & she loved the little shows & the chances to meet characters in each country) You can spend a 1/2 day in FW & 1 day in WS.
Fort Wilderness has fun stuff at night such as a hayride, campfire sing-a-long with Chip & Dale (I'll warn you, my 1yo was scared of non human characters!), and a movie (go to the camping thread at the beginning of Sept for the calendar of movies).
The above schedule allows for lots of "down" time to sleep in or whatever. We are not morning people!!
Well, have lots of fun with your planning! You've certainly come to the right place! I asked zillions of questions last year at this time & honestly, I could not have planned it w/o the help of the DIS. I got so many great tips that I now feel like an expert!! And I love helping out the newbies!