For the diffuser, there's a nice one or two in all LED/OLED monitors. More stuff in there too, acrylic/polycarbonate glass and a Fresnel lens. Worth scavenging if you come across a broken one.
Oh that's a great idea! This also reminds me of the video where the guy took out the LED panel and used just the light and the Fresnel lens to make a window with very natural-looking light.