for either tank either substrate will do but most prefer sand, and or a deep sand bed (DSB) 4" deep as this will help eliminate nitrate buildup. The main knock on CC is that it traps detrious which create nitrates and it does nothing to reduce nitrates. more importaly is your lighting needs. If you may or may not start a reef you might as well start with sufficient lighting to at least have soft corals or LPS. Depending on your tank size a VHO or PC lighting system would be a good way to go and you could always add MH later when the SPS coral and clam bug bites you. Easiest starter corals are mushrooms as they are hardy, colorful, and cheap. Go slow, have fun, ask allot of questions along the way.