Like others said, we won't know the schedule until parties start. Even then they can and will change times (like parades, characters, etc). I've never tried to get FPs using a party ticket (always had an AP), but I would probably just not do FPs altogether. They would only be available for the 3 hrs where the park is open to regular and party guests. And during the party there will be such short lines they won't be available or needed.
Will you be going to the parks other days or is this your only day? If it's your only day you may want to check out California Adventure for all the new Halloween stuff during those hours (of course it could be pretty crowded with lots of party goers doing that). That would allow you to spend the whole party time in DL.
When it comes to the party itself once details and schedules are released you should decide what your priorities are. Do you want to see rare characters? If so, you'll need to be prepared for long lines. Trick or treating? Wait until after the first hour or so-the lines can be longer at the start but will be empty later, so don't waste time in a long treat trail. Rides? So short! We virtually walked onto Space Mountain and that was right after the party started. Make sure to watch the parade and fireworks-second parade is much less crowded, but you should absolutely make sure you are in front of the castle for the fireworks (they have things flying over that are best seen from the front). Cadaver dans are also on rafts in the Rivers of America, so it is cool to see!
We will also be there October 13th! Rain won't be a concern like Florida, but you may want to think about a sweater, because after dark it can get chilly in SoCal!