8x8x8' fish tank?

I just finished my 8x8x8 ft. fish tank, I have it all setup, now I just got to know what fish to add. I might add 30 various pygogenus piranhas, but im thinking of doing a few pb,a black and silver arowana, a jardini arowana, a couple motoro stingrays, an alligator gar, an florida gar, and a spotted gar. What else should I add?