Having gone to the event for the 1st time last year, I'll happily echo that Stay & Scream is a must. It's a real good way to get some of the more slammed houses out of the way (Stranger Things and I presume Ghostbusters), or from what I hear, it's also a good way to hit up the tent houses a good amount before it's open to the masses.
Having Express is also recommended, as that can not only make it easier to see all ten houses in one night, but on the more crowded nights, it could be a flat-out necessity! Now if you have Express, I generally don't recommend using it during Stay & Scream, that'll be a waste of a Express when it's more valuable during the middle of the night when lines are longer. However, there is one exception...
If you think you're not going to hit up Stranger Things more than once, then I'd use Express on ST the moment you're let out of the Finnegan's holding area. That's what I did last year, and I passed a monster general line into a downright empty Express queue, getting the house out of the way very quickly.
Also, a very helpful tip for Stay & Scream. SUNGLASSES. It's still going to be daylight when you're let into the houses, and I've read more than one occasion where people learned the hard way that their eyes won't adjust in time in a house. You want to be wearing your darkest pair during the day, and when you get close to a house entrance, you want to close one eye for at least 30 seconds or more. Keep that eye closed when you get in the house and remove your sunglasses, and once you're in a scene or two, open it. You'll be able to see much better and enjoy the house. An of course, have your sunglasses at the ready to put back on once you're out of the house.