In my opinion, any large angel can go well in a second tank if you must have another angel fish and not dwarf.
Your emperor angel will not remain juvenile. This is one of the most striking of all marine angelfish, but its important to provide varied diet, supplemental vitamins and color enhancing foods to ensure color vibrancy later in life. I've heard 3x daily feedings recommended. I can do 2x for my tank, but I'd need an auto-feeder to supplement if I needed more feedings like you. Also see if you can get it used to a variety of foods as adults reported to be poor eaters, so if you can get ahead of that while still juvenile, you'll have more options if it decides it doesn't like certain foods later in life.