I'm sure this has been asked before, but when I buy separate tickets for MNSSHP, will I also be using up one day of my hopper if I am not in the parks earlier that same day??
MNSSHP is a separately ticketed event (called a "hard ticket event"). That means that the ticket you get is your park admission for this. You do not have to use any days off your regular WDW passes to get in.