Your question is loaded with a lot of mis-directions and decisions not made
I know. it’s just an idea. I’m already sorted for sound, running 5.2.4, currently have a 55inch OLED which stands on a bespoke AV unit. The unit will not accommodate a bigger TV (due to other equipment) and my wife will not allow me to wall mount a TV - one of the very restrictions she has given me. I do not have the scope to put a rear mounted projector in the lounge, logistically too difficult - you’ll have to trust me on that.
I thought that an UST could sit exactly where the TV is currently and project on to a c100inch frameless screen. I’m around 3m from the screen/wall. I watch general TV or movies, never sport.
The other restriction is that it is a lounge, so I can’t paint it a dark colour. It is currently a very very light grey - closer to an off white. Also on a night, when most TV is watched, my wife is often doing other things in the lounge whilst I watch the TV, reading or looking at her phone - so she insists on having the lamps on, but they are not really bright and have shades that would avoid direct light hitting the screen.
I have had OLED and Plasma, so like my black levels. If a UST in anything less that complete darkness is going to a huge drop in quality, then I’ll just stick at 55inch TV. I’m not willing to sacrifice that much quality simply for a much bigger picture. All the marketing pictures show UST being used in very light environment and perhaps that is misleading me...