Good luck to you on your quest!

About that particular unit I don't know much, I will say there's a Great War Forum (if I remember the name correctly) that has very knowledgeable people on it.

As you mentioned oftentimes the best photos are found in the individual regimental histories, journals, and websites. My only issue with these is that they tend to use small images, little postage-stamp size pictures which would be fine for the margin of a journal...but it would be nice once in a while to have a high-resolution photo.