Epcot is all one park, the Showcase stays open later as it's where most of the restaurants are located (in the different countries) around the lagoon. The fireworks are then viewed around the lagoon before the park closes.
You don't have to move the car and can simply walk from one area of the park to the next.

Afraid I don't know the best route from Crescent Lakes but I'm sure one of the other owners will be able to give you tips.