Wonderfull fish, one of my favs, but they'll eat small fish and inverts. Full grown this fish gets big, and will probably require a larger aquarium.
Also, I would wait longer until you know your system is stable and can handle fish, rather than right after its cycled. You wont have a problem with most fish adding them first and the Harlequin later, but you might be restricted if you add the Harlequin first as they can get a lil attiitude (and generally run the tank).
I've kept several specimens and I must say that the ones from Australia have incredible coloration.