This is looking soooo awesome! I love experiments like this. If it works, fabulous. If it doesn't, a lot can be learned regardless.
I like the combination.
I like Hara species. They'll enjoy the sand. Would love to see a nice school of semi-agressives. Like Hyphessobrycon species, even Serpae. The salmon would look amazing against the greenery. 25-30 or so would be impressive. But not sure if they'd go with Hara, doubt it. The tank is large and very tropical. A tetra with more substance would be lovely, which is why I suggested the serpae. Black phantom, red phantom...
Tiger barbs, maybe if you wanted to go Asian. I don't know, I don't think these species are given their due enough. People complain about them so much that they are so agressive. Kept in the right numbers, they are an impressive display fish with more edge.
Just my two cents.
Liz