I would stay BLT lake view, watch from the park on 7/3, walk home that evening and plan to watch from TOTWL on 7/4. We were just there on 7/3 and the crowds were really not bad. It was nice that they did the fireworks at 9, instead of 10. Getting out of there was not bad, since a lot of folks stuck around to take advantage of the 1AM closing.
If you want to catch MK on 7/3 and then Epcot on 7/4, then I would suggest staying at an Epcot resort so you can walk or boat home after the show on 7/4. Epcot closed after the 7/4 fireworks, so the lines for the buses were much worse than those from MK on 7/3.