1) No.
2) Absolutely not.
3) Closed due to capacity is closed for everyone.
4) Your best bet for July 4th, is to get to the park late in the morning or early in the afternoon and "tough-it-out" until meal time.
. . . New Year's Eve is HUGE for fireworks
. . . Fourth of July is almost as bad
. . . I have yet to see a July-4th NOT be closed due to capacity at MK (other parks are ok)
5) EVERY YEAR people get rejected and kept out of the park for their ADR, thinking it is a way to get into a closed park.
6) Nope.
7) If it were possible to use the ADR as entry, LOTS of folks would abuse the privilege and just make an ADR to gain entry for the fireworks.
PS - If you make and ADR, and are shut out due to capacity closures, you will be charged the r$10/person No-Show Penalty, since WDW considers it you responsibility to arrive at the park in time and gain park entry. Plus, during such high-demand days, there is usually no "courtesy" or Grace Period for being late to an ADR, as there are so many others waiting. Your ADR can be cancelled and the No Show Penalty applies.