Well.....nothing will work better than Black Velvet to create the illusion of the Screen floating in space. However the right choice and proper application of Paint will certainly get you closer to that goal.
Any attempt at doing a righteous Zero Edge is dependent on being able to get the projected image dimensions to fit the Screen as perfectly as possible.
You have a W1080ST. It has no Lens Shift and among the shortest Focal length of any PJ. (1'-5")
So your first job is to get the PJ mounted at the distance you need to obtain the size you want....and that is something tied to your room / seating circumstances.
Once the PJ is mounted, you can shoot a temporary full sized image onto the wall where the screen will go, get it squared and true, then lock in the exact perfect size / dimensions for your screen. Because you only have 8' to work with, and a big screen in mind, ...also the desire for two rows of seats as well as Stand Up Gaming down front, you have set the screen's top edge as high as possible.
A metal framed screen that has a known thickness of components will easily allow you to hang is securely over such a pre ordained location.
Before you do....that's when you "SPRAY" on first 2 coats of a dark Gray tinted Primer, then spray at least 2 Coats of the Mouse Ears in a Flat or Matte Interior Enamel
If everything gels, and the image fits almost perfect, then most all overspill will first be scattered somewhat by the 3" drop of the Metal Frame, and the attenuated by the Black surface. But in my opinion, if this is to be 2.35:1 CIH, the intensity of the light spill (ie: non projected, horizontal image areas...) will determine as to if a paint will suffice. I cannot speak as to how well such areas are masked using the W1080ST. But one thing about paint. It can get covered with cloth if it's performance is found wanting.
As stated, the real success in it all hinges on your doing a highly adjustable and rock stead ceiling mount, and getting the screen matched up. If only you were painting onto the new wall, how much easier it would be and how much more effective the performance would be as well.
OOPs....wrong thread for all that business.