I would leave it as open as possible personally. It looks like you have mainly Aulonocara, which are open water fish. They would probably appreciate some caves, but I don't think it's necessary. Acei seem to do better in small groups, and they would need rockwork. I liked them in Mbuna displays because they like to roam the upper levels of the tank, but you have Peacocks. I would ditch the Acei as well. I like the lighting and substrate choices. Looks great.