Are you spending your day in the park before HHN starts? If so, take advantage of Stay and Scream. There normally is 4 location but one might be used for AP holder early access. It should for sure be the Hello Kitty area (formally Lucy), Diagon Alley and one of the side streets of the New York area. Basically, these locations will let you stay inside them while you wait for the park to be cleared of day guests. Typically these Stay and Scream locations release 20-30 minutes before HHN starts and the front gates open. Each location has a house that opens early, so whenever the park is clear and the house is ready, you are released and led to the first house. Stay and Scream is a GREAT way to knock out 2-3 houses before most guests even get into their first house.
I personally suggest the Diagon Alley area because they sometimes keep the ride open but the shops and restaurant remain open during Stay and Scream so you can shop and eat while you wait and possibily ride Gringotts!
If you are not going into the park during the day, you should be able to use the hotel guests entrance but it opens at the same time as other guests.
As far as AHS goes, its just a rumor but it is looking more and more likely to be true.
Enjoy your first HHN! I had my first two years ago and I am hooked! By far my favorite theme park/horror experience ever!