Tangs or cockatoos, eh?
These fish require entirely different water parameters to breed. I would do some testing on the water from your tap to see how hard it is and what the pH is. If it is hard and alkali, go for the tangs. If it is softer and acidic, then you could do cockatoos or tangs if you want to supplement your water with baking soda and epsom salts. The less you have to modify your water, the more stable the parameters will be, and the happier your fish will be. And happy fish make more happy fish. HTH.