My husband and step-D (age 15) really only care about rides, although we will be doing most of our dining, parades, nighttime shows together, but split up for shows or M&Gs that they might not want to do. So they would be hoping for some shorter ride lines at the party for attractions that may be extra busy during regular park hours. Is there virtually no wait for the rides during MNSSHP?
So, for this trip, while my DD may want to trick or treat and I would want to watch the parade and Hocus Pocus show, I don't think she (or I) will care about meeting special Halloween characters UNLESS there are princesses at the Halloween party that aren't normally at MK or if the lines for say, Rapunzel and Elena are shorter than usual. When will they announce or when can we find out which characters will be available for M&G? Since our ADR for BOG wouldn't be until almost 9, we would have a good two hours of the party for rides and M&Gs, maybe some trick or treating, although I'm not sure how much we can get done in two hours. Then assuming we can eat by 10 or so, we would have almost two hours after dinner. If I knew that we could quickly meet Rapunzel and Elena during the party, then I might skip getting FP for them on another day. I mainly don't want to miss any of the special parades, shows, or fireworks because of the time of my dining reservation, but there are no times out for Hocus Pocus or the Parade yet, just HalloWishes.
It sounds like you have a good idea of what everyone in your group is going to want to do. We have been to two Halloween parties and two MVMCPs, so while every year is a little different, I will tell you about what we have experienced related to your highlighted questions above:
RIDES: In my experience ride lines are much shorter during the parties with waits for the more popular rides of 10 minutes or less and walk-on for everything else. The exception to that is Seven Dwarfs Mine Train, which still sees pretty long waits (around 30 minutes or so) for most of the party. We have been able to go directly to SDMT after the second parade and ride with a minimal (10 minute or so) wait. It's also possible that BTMRR may have a little bit of a longer wait this year with Splash being down - but Splash during the halloween party is walk on (I think because people may not want to get their costumes wet?), so it may not be any different than previous years for BTMRR.
BOG ADR: If you really want to eat dinner at BOG, by all means keep the ADR - but it may mean that you have to miss something else from your list. Whenever I have eaten at BOG, I have never gone in right at the time of my ADR - it has always been as little as 5 minutes late and as much as 20 minutes late. They tend to get backed up during the dinner hour and so with your ADR being later, it may mean it's even more likely they are running behind. You definitely don't want to feel like you are rushing through dinner to get to other things or it won't be a good experience.
CHARACTERS: The long waits will definitely be for the characters that are not out any other time of the year or are in costumes when they usually aren't. I haven't tried to meet the Fairytale Hall princesses during the party, but I am confident their waits are likely lower than they would be during non-party times. Sometimes in the past they met with their princes and then the waits were longer. Others may be able to chime in on that. If they do have any princesses out that aren't out other places for the party, you will want to watch this thread over the first few parties and people will post how/when/the best strategies for meeting that princess.
PARADES/SHOWS: You note that you definitely don't want to miss any parades/shows - this leads me to suggest even more that you reconsider your BOG ADR. Last year, the first parade was at 8:30, Hallowishes at 10:15, and the 2nd parade at 11:15. The Hocus Pocus shows were 9:15, 10:40, and midnight. The area in front of the castle is mobbed all night - it's the most crowded area of the park, so navigating in, around, through it is pretty difficult - so even if you get out of your ADR around 10:00, getting to a viewing spot may take some time. We have had success with getting a space around 9:30 for Hallowishes (we sit in the area that they use for the dessert parties/old FP+ area near either Casey's or on the other side of the street). We then head to liberty square or frontierland to find a place for the second parade and then watch the last showing of the Hocus Pocus show at midnight. The only time I would suggest the first parade is if there is rain in the forecast for later in the evening (we missed the christmas party parade one year because of this!).
Of course - we won't know much about how similar this year is to previous years until after the first party, so you might want to hang on to your BOG ADR until then and then make a decision on what you want to do!