Quote (theQ on Dec 10, 2014 1:17 PM): 1. What is the best place to buy ? Amazon sells 120" for 900+

For an AT screen, I would contact Seymour AV directly. They may be able to work with you. There are other AT screens out there, but I'm not familiar with all, or even most, of them. Some are better than others, so do some homework. You can also built a screen yourself if you buy material from Seymour AV.

Quote (theQ on Dec 10, 2014 1:17 PM): 2. Do I need to paint black behind the screen ?

It is typically recommended to have a dark wall behind the screen. You could buy a black sheet if painting the wall isn't going to happen.

Quote (theQ on Dec 10, 2014 1:17 PM): 3. Can I have Left, Right, Center behind the screen ?

Yes.

Quote (theQ on Dec 10, 2014 1:17 PM): 4. Can I see the speakers thru the material ?

Depends on the screen and the material. But, it's recommended to leave the grills off the speakers, and to paint the frames of the speakers black (or dark) to help hide them.

Quote (theQ on Dec 10, 2014 1:17 PM): 5. Can you confirm the 135 would be ok for an average viewing distance of 13 feet ?

I am okay with that size personally. I am a big fan of try before you buy. That is, if you can, get the projector, and shine an image up on your wall and sit at 13' away and see what size you like best. I think 130" or so would be fine. But, that's me. You may prefer 120". I just had a client who is sitting about 10' away and they are happy with 134" from that distance.

So, don't get to hung up on screen size. Most people get used to almost any size which you put up on the wall.