I don't think a sump is absolutely required, but it sure does look a lot nicer than having equipment and cords hanging all over the display tank.
It's also extremely convenient for water changes!
Nice looking tank, I don't have enough courage to put 4 big fish in a small tank. I want to try a larger fish like a foxface or a kole tang...but I just don't want to risk it. Have you had any nitrate problems or fish fights?