If you haven’t already read through this, I highly recommend it Disneyland Mickey’s Halloween Party 2018 Planning Guide
Right after it talks about the fireworks show, it talks about characters beginning with a section on the ToonTown Pre-Party (that is a lot of fun!) and then also lists the 2017 characters that were available. One note about how they listed it: The Pirate Pals on the Frontierland Dock & Mickey & Minnie next to the Petrified Tree were all one line setup when we did it. They rotated Peter Pan/Wendy with Capt. Jack Sparrow and we got Jack Sparrow. You had the option to skip that first meet if you just wanted to continue on waiting for Mickey & Minnie OR if you just wanted the Pirate Pals you could exit without continuing on to wait for Mickey & Minnie.
Also, when they say Jack & Sally’s line gets crazy they are not kidding (really all of the Halloween specific characters get crazy including the ToonTown pre-party where the characters are dressed up, Peter Pan/Wendy because Wendy only meets during the party & the villains. Winnie the Pooh is dressed up as a bee & is super cute & that was probably our shortest character line all night. Jack & Sally can be seen during regular park hours & we have often done their wait with 20-25 min. waits by going just a few minutes early for one of the earlier posted meet times on the app.
Near the end of the night, the villains all came out on the train station to dance to Halloween music & that was one of our favorite things (it’s not really announced or listed anywhere but I have heard of it happen before & was glad we happened to catch it). Afterwards, they went back to do their last set of meets & we got in line for Maleficent & even though the kids all passed out in their strollers in line (it was 11:30PM so no surprise), they specifically told us before that we were not to leave Disneyland until we got a picture of them (even sleeping) with Maleficent.
And then about your fireworks question, in the street in front of the photo shop is a great place. But make sure you move out into the street. In front of the Photo Shop on the sidewalk isn’t fireworks viewing & they will ask you to move to keep walkways clear (and there are trees blocking a great view from that angle anyway). They setup a roped off walkway that allows traffic to cross Main St right there, but that will be one of the bests places for your DD8 to get an unblocked view.