If ya place a thin layer of sand on the bottom, you will get light reflection upwards towards the undersides of your corals, this will help. The black bottm should not cause any heat retention, or increase in temperature.
-dave
I'd stray from acryllic, it will scratch on you. Acryllic will also bow a bit when filled. Especially with acryllic algae magnet, picking up tiny grains of sand. I'd go with STARFIRE glass. There are several custom tank makers in canada and the US, try searching on the web.
-Dave