the butti prolly doesn't feel threatened yet. that prolly y it hasn't attacked anything yet. so, say a similar size fish is introduced or one of the tank mates gets bigger, more closer to his size. then prolly will have issues. i had one before was housed in a 75gal, with several other africans. once he outgrew everything, it were on a killing spree, one at a time. i also have seen these fish over 12inches. big males. i feel that since yours is larger then the rest in tank for now, might be the reason he isn't interested in the others.
my advice for "if you do get a female", is to set up the other "breeding" tank, and keep her in there first for awile, and beef her up. then introduce the male into "her" tank. use a divider for first couple days, if nasty fighting occurs.
if you put him in the "breeding" tank first, he will kill her without a divider. because then that tank is deemed his. and will fight for his home, to all comers.
well gl. and take this info as you will. :dance2: