S.H.
In december we managed to go to DW with a family of 6 for 9 days 8 nights for about $3000. We stayed at the moderate resort....went during the free dining offer.....opened up two SW visa cards when they had a promotion (paid $400 for five RT flights from Phx to Orlando, my dh is a pilot so he flew free). All the meals were paid for and we had almost $300 reward dollars from the disney card. We will NEVER be able to go that cheap again, but if you do some major planning it can be done.
Go to disboards.com.....it is a wealth of information.
If you drive, staying off site is a good option, but staying onsite is wonderful. Especially at smaller resorts with less bus stops.
I would go at least 3 days....you will not get much done. Those three parks are good ones for the three days. The longer you stay....the slower you can take things. You cannot see it all, even in two weeks....so just plan what is most important for you to do and the rest is just icing on the cake.