Hmmm, that trigger should be in a 70G or larger tank, the tang should be in a larger tank too and I'm surprised the trigger hasn't been nipping the lion. I don't think you should add any more fish to that tank. Are you planning on an upgrade?
You should be able to keep lower light corals.
rating is the spectrum of light, 6500k is yellow, 10K is white and 12K starts getting blue (i think...drawing a blank here, for some reason).