Excellent! You're all going to have SUCH a lovely time! Seven months is plenty of time to plan... but I'd suggest the first thing you do right now is look at the projected schedules for opening/closings and plan for any Advanced Dining Reservations you'll want to make. The reservations open up 180 days out, but if you are staying on-property, I think you get a 10-day jump on that. I'm not sure if Fort Wilderness is included in that, but either way, it's coming up soon.
There's a LOT of Loooonnnggg tip threads you'll want to read through... but they're worth it.
One tip I wanted to offer is that I see you're bringing your princess. When I took mine, we planned to start our vacation with a trip to the Bibbidy Bobbidy Boutique on our arrival day... there's one in Downtown Disney, so we did that before we even checked into our resort... there's no ticket required and free parking, so even if you're not planning to do BBB, Downtown Disney is a great "first part-day." Plus there's a HUGE World of
Disney store there where you can see a LOT of merchandise all together... It's a good idea to window-shop there the first day, then do all the parks, then return at the end of your trip for anything you still want. (And I'll get flamed for this, but if you have the transportation available, do check out the tourist-junk shops in town!)
I can tell you, and many here will agree, planning is half the fun! By the time we finally took our trip, I had spent a year planning it, I had a daily schedule for which park we'd be at and which reservations or walk-in places we wanted to eat at and the times for those... but not a by-the-minute stressful deal. The trip itself was WONDERFUL because it was the culmination of so much planning and dreaming. I hope yours will be the same.
While you are planning, it's time to start shopping!

Keep an eye on Dollar Tree, Target Dollar Spot, and the yard sales and thrift shops. Disney stuff shows up there all the time! If you can find a (non-icky) Minnie Mouse headband for $.50 at a yard sale and tuck it away, that's money you can use for something else when you get to the parks!
So off you go! Get started reading those Loooonnnnggg threads! I promise they're worth it! Oh, but DO plan to bring a stroller for your nephew and possibly even for your daughter. They WILL get tired, and it's expensive to rent them, plus you can't take them out of the park if they're rented. (Plus they are handy for hauling around all your junk!) We saved a TON of money on snacks and beverages by bringing in our own each day and just hanging the bag off the back of the stroller. No way would I have wanted to carry that much weight in a backpack, though!
I'm also sending you a PM.