Yes, you can add a few more equal temperment, equal size fish in there. You only have three fish so far, another 4 would be alright in a 180, plus a bottom dweller or two.....Count out the TSN, RTC and ARTC for size, plus once they get to large, your fish will be fish food.....Stick with something that reaches around 14-18 inches in length, maybe less. Butti's get huge though and they are mean, but the red devil and depending on what type of pike you have, should be fine.
You can try some Parachromis species.....Motaguense, Managuense......wouldnt really recommend Dovii because of temperment, maybe another Pike would work, again, depending on what you have now, just make sure there is enough hiding spaces......A lugubris species would look nice in there, like a cobra or cincta.