A:Answer I am currently projecting onto a 120" (measured diagonally) screen and the image is superb for 4k movies. You would have to sit farther away from the screen if it were 180" (measured diagonally), but I don't think there would be much loss of quality if you sat the recommended distance from the screen. Also, with this projector you would have to hang it between 14'-9" and 19'-2" for a 180" (measured diagonally) screen.
If the room will be dark whenever you are watching a movie (no outside light from kitchen or windows), then you wouldn't need a projector with higher lumens. Otherwise, if the room will have a lot of light coming in when you are watching movies, then a projector with higher lumens will help a little bit, but just note that most projectors suffer in quality in a brighter room. My current setup is in a basement with three windows (all have blackout curtains on them), and it looks great to me when I watch during the day with the lights off.