We are going for our first ever HHN visit on October 9th, it will be very busy with the Saturday / Holiday weekend combination.
We plan to get Scream Early tickets. We already have single day tickets (for HHN) and Express Passes.
Can someone fully explain how the Scream Early works? What is the full benefit (in regards to HHN)?
Any tips on food for this event? We will need to eat, but want to maximize our HHN house / zone time.
Great replies above to your question.
I'll add that since you are going in October (we are too), you will be able to read what people's experiences are in September and the first week of October.
Historically, the Stay and Scream areas are at Finnegan's, Simpsons, and Hello Kitty. I think they used Diagon Alley before, but I'm not sure.
Anyway, if you are getting there a few hours before regular daytime closing, you might be able to get food during the wait, but there are lots of people doing the same thing. Might be able to or might not be able to. You might want to consider (though again see what people report in September to help you decide all these things) eating earlier at City Walk before Stay and Scream. You can also use the SaS time to get a ride or two in before HHN.
Since you have HHN express, you can take a quick break for food during the night (we usually snack a couple of times each HHN night and go on a few rides between houses). Note that Diagon Alley is open most of the night (it usually closes early though) and it is a great opportunity to ride Gringott's without too much wait and get ice cream if you want.
As for the release, once they clear the park of non-HHN ticket holders, they will release the SaS people from their holding areas (before opening the gates for people waiting outside). You can rush to the main soundstages (near Rip Ride Rocket and the Tribute Store), the back houses near Men in Black, or the houses in the Kid Zone (again, see what people say in September to get a better idea how things work this year).
Some people don't use their express passes on the first house or two and repeat those houses later with express. Depending on your stamina, this can work for you or you might want to go ahead and use express passes immediately. We've done both, but we usually just start using express right away so we have more time to enjoy the scare zones and have more food/rest breaks throughout the night.
If I only had one night, and it was October 9 (which as you said is expected to be very crowded), I would eat before going in the park and focus on making sure we were able to go through all 10 houses and spend time in each scare zone. After a couple of hours, you should be able to gauge how much there is left to do and be able to decide how many rides and breaks you can take based on your stamina and time you want to leave.
I'll strongly recommend again to check back for reports from September and then extrapolate those reports for more crowds in October. I'll say that in the past 10 years, using express passes, we have been able to experience it all, if we want to. Sometimes it has been a long night, and sometimes it has been a not-so-long night. Please, though, make a priority list of houses, scare zones, rides, food, drinks, breaks, etc and make a loose plan. If your group is at all stoked for this event, you will have a great time. It is fantastic. Your feet might not like you in the morning, but the memories will remain.
Good luck and have a great time!
EDIT: I totally forgot to mention that you may or may or may not want to pad time for the show(s) during the night. Noting has been announced, but there is usually a show or two. Sorry about that.