I probably also have around 16-20. But, unlike you, I don't distinguish so much work, clients, and evening, and (in the summer) casual shoes. I do however want to have a few both light summery, and heavy wintery (ie I don't mean winter shoes, but nice, semiformal shoes that have nonetheless a thicker sole and are made of heavier materials). Also a mix of black and browns, plus some summer mocassins or the like in light colors (I live in a relatively warm weather).
cacio