July 4th is the second busiest day at WDW! My son and I celebrate our birthdays July 2 &3, and we'll never go there again for our birthdays.
I'd recommend you avoid the MK altogether, since they closes it to admission the time we went. They had hit the max occupany by 2 PM, and we left having ridden only 2 things all morning. EPCOT had awesome fireworks (beyond Illuminations), was less crowded (but still crowded...), and we spent a few days mostly swimming. The crowds died down after July 5th...
steve