According to my calculations (72" x 18" x 18" = 23328/231=100.99) this is a 100 gallon tank. A 125 should be 4" higher.
I have a 150 gallon reef ready tank and I use a the Nova Extreme Pro T5
12 bulb T5HO unit. Each bulb is 39w. This works great for me. I keep LPS and softies, a few fish and two anemones. I have yet to try keeping SPS under these lights, but I have read about others doing it by keeping the SPS higher in the tank. At 18" deep I think that you would be able to keep them at any height, as long as they weren't shadowed. The corals you mentioned are LPS and softies, but think about the future; you might want to go SPS. You might as well be prepared.
Metal Halide have the benefit of light penetration in very deep tanks. They also give off more UV light that is essential for zooanthelle growth. I have found the Aquaticlife HID/T5
fixture, which uses High Intensity Discharge lamps, and the ballasts are all inclusive. This fixture boasts having the light intensity of metal halide without the heat exhaustion. It also has a built in timer. If I had $1100 I would buy this light in a heartbeat.