can't help with the build but most modern onboard graphics chips and motherboards support 2-3 discrete monitors. vga, dvi and hdmi, so that side of things shouldn't be a problem.

There is an english company that makes dlp 3d printers who have made printers with build playes as large as 50 inches. But I believe they use led screens rather than projectors.
Given how cheap and bright a modern led tv/monitor is - that might make more sense and have a bottom up approach instead.