First off, I do not suggest you use 3mm Sintra. It is very floppy, and easily transmits any irregularity beneath it, be it wall texture, adhesive, lumps, bumps and boo boos.
I know it's tempting due to price, but unless you have a perfect wall, and use a brush-on adhesive, it probably won't end well. 6mm is the "go to". Ask your supplier if he has any similar "Sign Board" material (Komatex, etc)
Screen size-wise, using a 60" x 120" sheet of something, the biggest 16:9 image you can get is 122" diagonal (60" x 107")
I suggest that with the VPL-HW50ES that you mount the unit at 13' for maximum lumen / foot lambert performance, and use a Silver Fire v2.5 4.0
Hanging the Sintra before Drywall (painting it elsewhere) is up is not a great idea. Painting the board in place is the ticket, even if you must mask off the walls / overhead ceiling in thin plastic (...like most do anyway...)
Besides having to worry about the logistics of creating a good place elsewhere to paint, the Sintra would need a Frame. If you used 3mm, it would have to be a substantial frame and even then you might see impressions of the framing transfer though. Not so with 6mm. And...when you move the screen, you must guard against smudges and such (...or worse...) and of course, if hung temporarily on Brick, "IF" the Face of the Brick work is level, you'd best be suited for the use of a diagonally ripped 1 x 8 to create a French Cleat held on the wall with Mortar Anchors.
Lastly, if you wait until Drywall, you can please the Wife with a 135"er (66" x 118") by painting onto Drywall. Or....purchase a bolt of Flexi-White Material from Carl @ Carlofet, http://www.carlofet.com/projector-screen-material/flexiwhite-projector-screen-raw-material.html
.....as it can be stretched onto a much more easily made frame, one that is far more lightweight, easily hung, and receives a painted coating every bit as easily and well as Sintra. Ask for it to be shipped on a Roll...and tell him you off AVS.
As I see it, if you hasten...your going to make much more work for yourself. Reconsider your options as far as timing. Everything else is looking good though.