Which home theater projection screen fabric?

I bought a 4k projector.  In looking at screens, I'm finding that many of them cost more than the bloody projector, and all of them are WAY too big.

So instead, I want to buy the fabric and just make my own frame like I would at the theater.  Problem is, at the theater I'm using a projector for a 20-foot screen and simply blasting it with 15k lumens and an XGA signal, so for that matter I could use drywall and cheap latex paint.  I don't know about the finer points of projection fabrics.

Here is the projector I bought.  Nothing crazy special, but true 4K, HDR "compatible" but not true HDR.  2200 lumens, and editor's choice from a few sources.

Here is the screen fabric I was considering.  Should it even be fabric?  Should I maybe just do some drywall on a frame and use paint like this?

Screen needs to be no more than about 36" tall, so somewhere in the 70" diagonal range.  Projector will be about 9' throw.  Room has plenty of ambient light (four windows) but has all-but-blackout curtains.  My calculations say that 2200 lumens on a 70" screen should be just fine, even with ambient light.

I'm aware of screen gain, and how the texture affects viewing angle, but what I don't really understand is why gray vs white vs off-white.  What are the properties of screen fabric/paint and why do I want one characteristic over another?

 Here is a good article for information about the paint although i have no experience with it.  

https://reviewscon.com/best-projector-screen-paint/

As far as the material, i use my projector mostly for camping. I actually use a polyester/nylon white shower curtain. It works great and looks like a proper screen. If you go the DIY fabric screen route and will be using it without the room being completely dark. Attach black fabric to the backside of the screen. This will improve the picture when the room is partially lit.  

Thanks for the link.  I'm fully living up to my normal modus operandi... researching the crap out of something.  I just don't want to spend decent money on a good 4K projector and then not see its potential when I project it onto a bedsheet, but also don't see the need to spend more on the screen than I did the projector.

Fun fact, the weave of the fabric actually helps determine the angle of viewing.  Since it's a cheap method, I might try some of the DIY paint methods and compare them side by side.... paint one piece of material with three or four sections of different paint formulas and see which one works best.

Here's what Came from my research. 
paint the screen paint on a mirror. I don't remember the specifics, but a small portion of the light is reflected off the paint, but, a lot of it passes through paint and gets reflected off the mirror. Because it's kind of back lit, It's close to having an actual TV screen, but 'UGE!!  
the trick is usually finding a mirror large enough. Find a health club, dance studio, or a strip club closing down and you can get mirrors cheap. 

That's twice I've heard that.  Interesting.  Not sure how I would get paint to stick to glass but it is intriguing.  Especially the strip club part.  That might involve extensive field research.

This screen will need to be portable.  Fortunately it will only about 73" diagonal, but that's still a lot of glass to be moving around.