For a first visit I think havin a look at a guide book can be a big help, just for a complete overview, and then everyone here is always wonderful for filling in the details! The Unofficial Guide (from the Touring Plans team) is pretty reliable, and I can always get my hands on it at our library.
We have two young kids (7 and 3) and although I pre-booked ADRs for a lot of meals I can guarantee we won’t use them all—some days last trip we didn’t do any table service, and were totally happy. The kids are itching to get out and do Disney stuff, the adults are tired, sitting through a long meal is not always fun (but in September you may appreciate the break in the AC!). Every night we reviewed our plans for the next day to see how everyone was feeling and if any pre-booked meals still appealed. We changed a lot of plans the night before (and a lot of even hard to get ADRs opened up the night before, too, so lots of folks changing plans!), usually cancelling a meal rather than adding one.
We found our best window for a sit down meal was actually sort of “brunch” time—and if you’re considering any character meal buffets, I’d highly recommend a late breakfast seating when paying OOP (lunch prices are much higher). We’d have a light breakfast in the room, tour while crowds were low, then go sit and eat while the lines were long. Hit another FP or two after brunch and then head for the pool/nap break. Then either a light early dinner at the hotel (we really liked the pizza at POFQ, I think we did that twice for dinner!) or grab something QS when we’re back in the parks later.
We also relied a lot on snacks, especially on hot days when no one was hungry enough to eat a full meal at once. We packed our own, but also supplemented with the many tasty snack options in the parks. That would have left us too full for a sit down dinner many nights!