Hi Muskoka!
I'm not in the co-op, but i'm waiting for the call to artist, maybe my response could attract others.
They ask for as many images as possible, but i think that 100 photos might be enough. not more, i think.
I also think that if you have 50 really strong and stunning photos and 50 weak photos is better to be rapresent with the powerful ones!
I hope that my english is good enough to be understandable

Good luck!