Without knowing specifics about your family, I'll tell you our faves.
Resort - Port Orleans Riverside
Park - We love all four parks but Magic Kingdom is our favorite because it IS Disney World. You can see & do everything at Animal Kingdom in one day, Hollywood Studios in one day but both MK & Epcot require 2+ days to cover everything.
Restaurant - This is a tough one! DH loves O'hana because he's a total carnivore! We all love 50s Prime Time Cafe & Hoop Dee Doo Revue. For character meals, I suggest Crystal Palace & Chef Mickey's. 1900 Park Fare has great character interaction but we were disappointed in the food.
Weather - We always go in late May/early June so I'm no help with December-specific questions.
Spending money - This varies greatly from family to family. My DH can go all week & never spend a dime. I love to buy new tees, hoodies, photo albums, year magnets & whatever else tickles my fancy. DDs all earn their "Disney Dollars" in the months leading up to our trip. I've seen many people on here say that they give each of their kids $25-50 for the entire trip. Our DDs usually have around $200 each. They all collect pins & like to pick up a new tee or three while we're there. It doesn't take long to add up! We always do the regular dining plan so we don't have to figure in money for food, just tips at the table service meals.
My #1 tip is, like many others will tell you, be at the park before it opens. You can see & ride so much in that first hour. It's totally worth setting your alarm!
Hope this helps!