We Stayed and Screamed last year but paid full price because I was so antsy to get my tickets (we went on actual Halloween). So yes, if you have regular HHN tickets and you're in the park - you're in. I've heard that you can get the discounted tickets at your hotel, if staying on-site, and I THINK someone mentioned last year getting them on the web site, but closer to October.
Re making reservations - we certainly didn't. There weren't huge numbers of people staying, and we ate at the Enchanted Oak Tavern - and it seems to me that might have been the only place open to eat at. We got checked several times for our tickets - methinks wrist bands would be a good idea...
Of course, since this year both parks will be open, it changes everything! I would suspect Stay and Scream people will have to stay in one park (seems like that would be an even bigger pain for security if you have people going between parks before 7) and again probably won't have many choices for dining.
if you have the prefered AP then you can get the HHN tickets for $32.75 each person, each night. ( plus $3.00 for S&H ) and i am pretty sure that the HHN FOTL passes will be offered at a AP discount price 2!! well worth the 180.00 price tag.
So far i have saved
HRH club level per night ( 6 nights for DH and i,
then 3 nights for Dad and GF ) club level for all =$918.00
HHN passes ( the 4 of us going 2 nights ) =$204.00