Well from the fish you've chosen it looks like you are shooting for a Brazilian Amazon setup. There are several species of apistos that would fit into that tank, but the only issue would be the silver hatchets in a tank that size. You might want to instead shoot for marbled hatchets they are much smaller.
But if you want a really nice centerpiece I would suggest Dicrossus maculatus and despite what is said about care, they aren't any harder than any other SA dwarves.
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