Head on over to accessories4less.com to get the
Denon AVR-1713 for $299 ! It's got 5 amps, 6 HDMI inputs, 1 HDMI output, AirPlay, Network streaming, and Audyssey MultEQ XT auto-setup and room correction. Should be perfect for you
Monoprice.com has very inexpensive
projector ceiling mounts .
For the screen, I'd highly recommend Da-Lite's "High Power" fabric, since you have white walls. Da-Lite High Power is a retro-reflective, high gain screen. Retro-reflective means that it reflects light straight back to where it came from, rather than bouncing the light off at an angle.
Think of the way a billiard ball bounces off the side of a billiard table. That is "angular-reflective", and that is how most screens reflect light. Now think of a stop sign. The light from your car's headlights bounces right back to your car. It does NOT bounce off to the side. That is retro-reflective.
So when you have white walls, you want the light from the projector to bounce straight back, rather than being scattered to the side walls the way most screens would do. And any ambient light will get bounced back to its source, rather than being reflected into your eyes and making the image from the projector appear duller and washed out.
Da-lite offers several types of fixed frames. Mate any of those with the High Power fabric and you'll be good to go!