Just buy some dry live rock. It isn't really alive anymore but it's cheaper then getting actual wet live rock. Then If you have a trusted LFS that has a marine section, ask them if they have a small piece of live rock that they can sell to your for cheap. This will seed your tank with microorganisms and bacteria. Also I'd advise getting not getting a panther grouper as they get way too large too fast, and you run the risk of your fish getting eaten. Instead look into getting a large wrasse, most of them are very easy to raise and eat just about anything. If you plan to keep a lot of large beefy fish, look into getting a huge protein skimmer. They may be super expensive upfront but they pay for themselves in the amount of hassle they prevent by helping in keeping your water quality in check. If you have the space and money look into getting a QT system too. The marine parasites bite much harder than freshwater ones, and they can wipe out all of your livestock in a matter of weeks if not QT. If you can't look into preventive dips before adding fish to aquariums like safety stop by blue life. Also be ready to keep many medications on hand if you don't QT.