1.) Fireworks will be happening at Magic Kingdom on the 3rd and 4th, while Epcot and Hollywood Studios will be only on the 4th. But due to the crowds, the parks will most likely close due to capacity. So when making your plans, plan on getting there early and staying in the park all day.
2.) Stay Hydrated. It is very hot and humid this time of year in Florida. Disney allows you to bring your own drinks containers in the park, so you won't have to buy a bottle water. Also Disney does give out free cups of water, you just have to ask. If you are planing on having alcoholic drink, then make sure you drink a cup of water for ever beverage you have.
3.) You don't have to be in the parks to see the fireworks. Magic Kingdom has perimeter fireworks, and can be seen from Contemporary, Polynesian, and Bay Lake Tower's Top of the World Lounge. These places can pipe the music in, but the experience is worth it even without the music.
4.) Have a fun and great time! Don't let the crowds get to you. Take a break if you need to cool off in one of the indoor attractions.