Exodons are a great choice, but if you want piranhas; I suggest looking into a few of the serrasalmus piranha species. Most don't get as big as a red belly piranha, the only downfall there is they do NOT shoal/school, & must be kept alone. Heck you live in NJ right?! why don't you have a look at either Shark Aquarium, or Aquascapeonline, both are in New Jersey, & both have some pretty extreme fish. Overall, exodons seem to fill out what you're looking for though, one of my buddy's just started up an exo tank, & I can't help but be a little envious; and I own 2 decent solo piranhas!