This is why people hire interior designers.... except I didn't hire her, she's just so great!
I would never come up with these things on my own....
Tara's ideas: What do you think?
Behind door #1 - photo wall (you certainly have no lack of material) with square, black frames and lots of white matte. If you didn't need the sewing machine there, you could make it floor to ceiling. I recommend the 20.5 x 20.5 Ikea Ribba frame. It would really pop if you had a darker color on this wall - something in the same tones but a more dramatic shade. Would look very cool in all B&W photos - even cooler with some gallery lighting directed at the wall.
Behind door#2 - a photo rail. My Dad made one for my Mom out of mdf moldings. I recommend painting it the same color as the wall so that it becomes part of the wall. The advantage of this is that you lean the frames against the wall and there are no nail holes if you swap out the art. I personally like the layered-photo-look but you could space them evenly. Same story on the wall color.