Need help choosing 1080p PJ

I am searching for a projector and I think I have narrowed it down to Optoma HD20. My budget is under $1300.

Room: W: 19 x 16 x 8.5

The sitting area is at 16 and the PJ will be hung at 15. I can't move the setting area because there is a beam behind it but otherwise the area behind is open.

We will use the PJ to watch HD stuff from Comcast, Blu-ray movies and stuff downloaded from Web -- all via HDMI.

Is Optoma HD20 good option for this size room?

Is there a online tool to assist in where to put the PJ?

Does the screen material mater if you want a clean 1080p image on the screen?

What is the maximum size screen I can use?

any tips?
Thanks

Thank you for the link.

Is Optoma HD20 good choice or are there other PJ's available which are better? I have heard that the fan on HD20 is louder then others.