I am actually going through the same thing you are believe it or not. Some questions are very important to answer. I know you probably do know have a lux meter, however if you happen to get your hands on one that would be more than helpful. The kessil displays the output on the back of the box, but as the light ages you can't be to sure of the light being put off. I currently starting off with zoas, palys, and many beginner corals to test out the quality of the a80. I have had no complaints and I have seen exceptional growth in my zoas the past few weeks. I do plain on upgrading and buying another a80, to share the space and to give a more consistent, better growth rate. I wouldn't dive into full sps until you're sure your tank is established. As far as only using one a80, anything is possible. I do think it would be more difficult. Please send back some specs or your tank. That's always a great start.