That's a fish that grows super fast, eats a lot, gets very rough when feeding (bumbs other fish), and it is gorgeous when mature. 30 in a 125 with a sump will not be too much, not at all. Except you may want to keep only them - there is no need to add any other fish to "enhance" the beauty of the tank. Trust me - you will love them when they get big, fat and colorful.
Keep in mind that the colors vary greatly depending on the bulbs you use and how they are placed. The best coloration is when the bulbs hit the scales from the front but that is not practical.