Unless you are in a concierge room you wo'nt be in the main building. Nothing is more than a few minutes walk from anywhere at the GF.
You wo'nt be able to see the fireworks unless you have a lagoon view room. The Conch Key lagoon views are probably about the best for fireworks viewing.
Having a fireworks view room will put you further from either the pool or the convention center, you can't really be right next to all three.
The main building is just that. The lodges are the other buildings.
Sago Cay and Conch Cay will have the best fireworks views. Sago is close to the convention center, but farthest from the pools. Conch is in between. Some rooms in Boca Chica will have a fireworks view, and will be close to the pool, but farthest from the convention center. But like I said, from the farthest room to the convention center will only be a few minutes walk.
Anne