I also have an 80-inch screen and the projector is about 2.90 away (measured in the middle of the unit). Since the zoom range is not that large, you should orientate yourself approximately to this distance.
My bracket (ceiling mount) is a standardised one with 4 screws. I bought it over 10 years ago and it also fitted the BenQ.
I have owned the unit for 11 months and am very satisfied. Best regards.
It depends on what it can/must do. Personally, I would use this screen for a home cinema projector:
Elite Screens Aeon Edge Free (Fixed Frame, 92", 16:9)
But if you'd rather keep the wall free, then this one:
Elite Screens Manual (Hand Operated (Roller), 92", 16:9)