150-225 lb of rock won't fill the tank - there will still be plenty of room for livestock. If you have the space, you can put some of the rock in the sump, but the fish appreciate rock in the main display. Sumps don't generally come preloaded with skimmers, so you will have to do the research to find a skimmer right-sized for your tank. Post the candidate skimmers here and we'll give you our unbiased opinions. As far as other equipment, besides the usual (heater, thermometer, refractometer, test kits, etc) you will need sufficient lighting to support corals since you indicated you wanted to go in that direction. Whether it is "a few corals" or a tank full, you need pretty strong lighting. I guess the best advice I have is to not rush into anything. Research each piece of equipment, decide what makes sense, and then float that idea here. We don't sell anything so we don't have a vested interest in promoting one brand or type of equipment. Nevertheless, you will find a variety of opinions here, so listen, and then make your decision.
