you probably know this since you bought the clown knife but the tank is too small for a clown knife, possibly too small for a bgk and extremely undersized for an aro.. if you cant provide a 180 AT LEAST within 6 months then don't even consider it.
but for your question.. its a matter of the aros/ck's personality.. my aros for example doesn't touch live at all while some aros will go loose for some hunting.. I have had 1-2 inch tetras with my aros and they wouldn't touch them.. and for the waiting.. it will be a lot of that if you'll wait for a bgk to reach full size..