I can recommend some smaller cool versions of the fish you have that fit for you tank. For example, a blue gourami is very similar to silver arowana in their color and graceful swimming style. Your catfish can be replaced by the cool upside down catfish, clown plecoo, or Cory cats. Your cichlids can be replaced by smaller cichlids such as Apistogramma, Bolivian rams (though DEFINITELY NOT GERMAN BLUE RAMS), Keyholes, Kribensis, and some other peaceful SA dwarf cichlids that grow to up to 5 inches. Or in a 40 gallon you can raise a colony of jewel cichlids which is very beautiful.