Good morning,
Sorry to say that our touring group has been to Mickey's Not So Scary Halloween Party since 2007. Therefore, if anything has changed since, please forgive us.
As I recall, the park allows partygoers to enter at 4pm. Yes, the party itself begins at 7pm. The Boo to You Parade runs at 8p and 10p, so I recommend the latter one. I also recommend a great viewing spot for either is at the Main Street Train Station. If you decide to view it there, you can watch the entire parade coming down or going up (depending on which time you see it) Main Street USA.
Happy Hallo Wishes, the fireworks show is only at 9PM.
The seven dwarfs are usually near Dumbo. However, with the Fantasyland expansion, I'm not sure if that is still the case.
The Disney Villains Mix and Mingle at the Castle Fourecourt Stage is usually something like every 45 minutes. The cast will come down in front of the castle after the finale of the show for pictures only. Sadly, no autographs.
Several of the hit rides are open during the party. I suggest seeing them towards the end of your evening. Get your candy first!
*Note: I suggested viewing the parade from the Train Station. It is possibly the best view. However, you will not get candy during the parade from up there.
Hope this helps! And Good Luck!