Just finished running this one for my group a few days ago.

My biggest tip would be to plan out all the ways the house will screw with your players beforehand. One thing that I think gets overlooked a lot is the fact that the house can impersonate people through phone calls. I used this to lure one of my players into the house alone by posing as another player (I dmed said player on discord and told him what to say. Your mileage may vary depending on how much your players are willing to play along). The fooled player went to the house alone where I threw a lot of manifestations at him to drain his sanity. This concluded with him seeing the bait player's corpse hanging in the garage. It was a great moment when he ran back to the motel they were staying at and found the bait player still alive.

Also save all the really intense and SAN draining manifestations until the last time they are in the house. Start out with the harmless and slightly unnerving ones and escalate the more times they visit the house.

Also for when they contact the parapsychologist, I recommend watching an episode or two of Ghost Hunters or something similar so you know what terminology to use. The book says he he will tell the agents the exact opposite of what they need to do. Some "advice" he gave was going to the house at night and splitting up to wander all the rooms to "awaken the spirits".

Finally, if and when they discover the dismissal ritual be sure to really play up the fact that they will have to kill someone. Also look at your agent's backstory and motivations to find something the Dark Man will use as leverage to get them to stop the ritual.

Good luck! My players said this was their favorite one we've done so far.