You've got way too many fish planned for there, and a biotope is a re-created natural habitat, which in aquaria terms is recreating a river system (such as the Rio Tocantins, Rio Araguaia, Rio Tapajos, etc.) with a selection of fish species, not the whole continent; it's much more narrowed down.
6x3x2 is a beautiful tank size and probably my favourite because of the huge footprint, but it's still not that big. Given your fish choices I think something along these lines would be much more appropriate.
4x Uaru amphiacanthoides "Triangle Cichlid/Waroo"
3x Hoplarchus psittacus "Parrot Cichlid"
2x Hypselecara temporalis "Chocolate Cichlid"
1x Osteoglossum bicirrhosum "Silver Arowana"
1x Crenicichla sp. (Pike)
2x Atronotus ocellatus "Oscar"
Not my personal favourite fish choices, minus the Chocolates/Parrots, but it'll work. If you're looking to keep multiples of each species watch for breeding pairs.