I agree with the earlier statements about getting a larger school. With exos, the more the merrier for spreading out aggression and limiting the establishment of territories. You can still expect to lose a few here and there, but nothing too crazy.
As for tankmates, my experience has been that it depends on when the exos are added to the mix. I have had extended success (minimal fin nips and scale biting) cohabing exos with medium size cichlids, catfish, and even other characins when the exos were added later. However, I have found it difficult to add new fish into an exo tank. It seems like once they are established, any new additions are viewed as food.
Personally, I find a heavily stocked species tank the most exciting and rewarding method for keeping exos.