No need to start another thread.
In the brightest mode that projector can run in .projector central says:
The range of lumen output on the AX100U is exceptional. In optimized dark theater mode, our test unit measured 343 ANSI lumens. But in Vivid Cinema mode, which still retains exceptional color and contrast, brightness was boosted to over 800 lumens. And in Dynamic mode we were able to get over 1400 lumens without too much compromise in image quality. This would be ideal for a Super Bowl party where brightness in ambient light is all important, and small variances from color standards are not noticed by anyone. None of Panasonic's prior models in this line have anywhere near this range of lumen output flexibility. (The AX100U will actually generate lumen outputs higher than 1400, but we wouldn't use those settings for video viewing or gaming.)
Based on that and the 75 sq ft of screen you want in the brightest mode you will be at about 18 foot lamberts with a one gain screen.
When you throw ambient light into the mix then it gets tougher with that large a screen. What are your expectations of black level contrast. Because a DIY screen with that much gain may be sacrificing some of the lower end detail.
The paint you will need will be one of the metallic enhanced mixes like Silver Fire IMO.