Not sure about July 3 but last year on the 4th we were staying at BLT and I think (maybe?) they had some dessert party, which we did not go to - we were in the park. We saw the fireworks from the regular viewing area on the terrace outside the BLT lounge on some other occasion, but I think for 4th of July and New Year's you have to stay at the resort to go up there.
We were also there for New Year's staying at a different resort and could not go up to the BLT terrace to view it then because they had signs all over that you had to stay specifically at BLT to go up. But we did see the New Year's fireworks from the bridge leading to the Contemporary and, tbh, you get about 90% of the view you have from the top of BLT, especially if you care mostly about the fireworks and don't mind some foliage partially blocking some buildings. All the extra 10-story height buys you is a better view of space mountain and Tron buildings. And that viewing area is free...
Here's what I mean:
Don't get me wrong - the Wicked Wind Down is not a bad deal for what you get for the money. Maybe less so for those under 21, but it's still decent. We'd be happy to repeat that and in fact have one scheduled next month. But if it's to see the 4th of July fireworks from outside the park, save your money for a nice dinner at Narcoossee's or something like that and then take to the monorail or walk to the Contemporary/BLT bridge to see the fireworks. Or time a dinner at Narcoossee's around the time of the fireworks and watch it from there (al so a great place to watch from)!