a "shoal" of big pacus in a huge tank would be something to see. Clown knife for the mystery effect, and the tinfoil barbs...so nerve racking. That seems to be a nice choice.
I would add a nice big green terror on there, about 6-10 inches, the orange fins are just majestic, and the neon blue/green...adds color. And maybe the hybrid catfish, RTCxTSN.
That's plenty.