A few others have mentioned before. You need to have lots of lights (which you have with your MH), plenty of water flow, and all your basic parameters in check. I would make sure you can properly check Alk/Cal/Mag, PO4/NO3. This ensures your tank is cycled and your fish are living happily in the tank. Make sure you have no SPS eating fish like Angels. If you got that down, then your ready to try. Start with easy corals like Monti, Pocillipora, birds nest. Millies and other across are pretty tough for a beginner, you may be sending them to their death if you don't know how to take care of them.