A couple great resources are the boards at disboards.com. There are many sections, including a family section. Most of the sections cover planning. There's also the Mom's Panel through Disney's main site, but they take a long time to answer questions, but you can read up on good ideas.
I recently stayed a week at Disney (in March), plus I'm a former Cast Member.
Do you know about the birthday promotion? Since you're already going to have tickets, you can have other options to the free admission perk. I chose the gift card that is equivilent to a day's admission. I'm not sure how much a 1-day ticket would be for your daughter, but that's how much the gift card would be for! There are other options, too, if you didn't want that.
Where to stay on property depends a lot on your budget. There are family suites, so that is more than 1 room. My husband, 3 yo son & I stayed in a regular room at the value resorts & had plenty of room, plus we were hardly in the rooms anyway! It was tight in the mornings, but we made it work. I understand you have 1 more little body in there than we did, though!
I see you didn't mention going to Hollywood Studios. If I had to pick between Epcot & HS, I'd pick HS with the ages of your kids. They have the Playhouse Disney area with a show & meet and greet with various characters. I could give you great ideas on meals, too! We did a character lunch at HS with the Playhouse Disney folks & also a character meal at Chef Mickeys. We were on the meal plan, too. We also really enjoyed Whispering Cayon cafe.
At the DIS main page (not the boards) they have menus from all the Disney restaurants so you can look over them to see what you'd like.
If you stay in a value resort, you need to rent a fridge, or get involved in a fridge swap that is free. They have those listed on the DIS board I mentioned.
If you have any other questions or want further help, I'd be SO HAPPY to help! I LOVE discussing Disney & we're actually going back for a 2nd trip this December for a long weekend!! Just send me a message through here & I'll help you out or give suggestions.
Happy Planning!!! :o)