MM will probably have to chime in since he is more familiar with European paints, but you will need to provide details about the projector and throw distance to the screen in order to make an informed suggestion about paint.
I suggest that you read through this thread http://www.avsforum.com/t/1436181/110-diy-spandex-at-screen. When you stretch the spandex you only want to stretch it as tightly as you need to remove the wrinkles. Start in the middle of the width of the screen at the top and bottom and roll about a foot of spine to secure it and work your way to each of the ends, stretching slightly as you go. Next, start in the middle of the screen height on both sides and work your way to...
I was finally able to take some shots of the screen. I had trouble getting a shot of the whole screen; probably because I was using autofocus. The first movie shot was with all lights on full and the Epson 8100 on Theater Black 1 setting. The second movie shot is with the lights out. I hope this helps!
Make the frame 2" larger than your finished screen size. This will allow 2" for the trim to cover the screen and still wind up with the screen size you wanted. The 2" overlap allows the trim to be nailed to the screen frame using finish nails that can be sunk into the velvet trim so as not to show. If you search the threads for "velvet wrapped mdf" you will find more info.
Remember to add 2" to each dimension of your frame if you want to add a velvet wrapped mdf border. I have a "zero edge" screen and it loos great too if you have a dark background. "Screen tight" is a good decision. It takes a little longer to do, but it makes it much easier if you want to experiment with silver over white for improved picture in ambient light or any other fabrics in the future.
Sorry, I managed to hit the submit button accidentally before I was finished. You should mount the projector at 12', which is within 6" of the minimum distance for that size screen. That will still only give you a brightness of 14 fl. That is quite watchable but if you watch with ambient light, you might want to consider a screen that is about 120" diagonal (59'x104"). The spandex will stretch enough either way if you buy the 4-way stretch material that is about 20%...
If you are doing a spandex screen for acoustic transparency you will only have a gain of about 0.8. Assuming that you are doing mostly TV and gaming and therefore are looking at a 16:9 format for your screen, the dimensions would be 120" wide by 68" tall for a 138" diagonal screen
You don't need to rotate either layer. Moire would be caused by stretching the material so that the texture of the weave shows. My screen is stretched more than it should be and I don't have any visible moire pattern. The milliskin (or moleskin) spandex has a very fine weave.