Arowanas, Knifefish, and Mormyrids. Those are what I'm primarily hitting for. Less Agressive Channa, Spiny Eels, Bichirs, and/or Plecos may be added provided I still have space.
The answer is 2. It's really hard to give a serious answer without knowing what exactly you want to put in it, as well as filtration and your maintenance routine.