Angelfish can grow to six inches long as adults, and have the same maximum height. They are quite intelligent, and will even take food from your hand. You could probably have three or four in a 55 gallon tank, and five or six in a 75 gallon tank (they are both 4ft long).
i have to add in whitecloud minnows and leopard danios. although they are all small (2" fullgrown) they are the goofiest fish i have ever owned. i have to fight them off when it comes time to waterchange they are so curious they try and play with the suction hose or my fingers. trying to net debris of the surface i have to constantly check twice i dont net one as they are so playfull they kamikaze my net. they constantly chase each other around the entire tank. they are definately the most fun to watch.