Today I spent my time editing the original vector art (within Photoshop), and then began working with editing the layer masks to look correct. Currently, there is room for three "photo" layers: two on the inside of the letters, and one in the letter outlines. After I got the masks correct for each layer, it made it incredibly easy to drop different photos in and try them out to see how they react to one another.
The photos I used in this version are by no means final (it's also missing a photo within inside of the letters). Tomorrow I hope to finalize the photos I'm using so I can create a final rendering of the letters; then, on Thursday, it's my hope that I can start experimenting with adding other shapes and photos to the composition/background, sort of like the master study photo. We'll see how that goes; I don't want it to get too crazy.
Also, I told this to Babcock, but it probably wouldn't hurt to post this here as well. As far as stock photos go, I've found sxc.hu to be particularly helpful. It doesn't have the greatest selection, but sometimes you can find usuable images, and you can download everything at full resolution if you get a free account. Pretty nice.