Much as I LOVE cories, I definitely don't recommend them for your tank. The substrate is just too large and they will hurt their little barbels on it. They do best with small, smooth gravel, or, even better, sand. Another problem with large pebbles is gas pockets forming - the cories eventually manage to shift some pebbles and get gassed in the face, which also hurts their barbels.
Definitely some ember tetras, though, when you have more cover. And shrimps. :) A bit of java moss tucked into some rocky crevices would make it a very nifty shrimp paradise. :)