I looked this aquarium up to get the dimensions, and they give 61cm length by 41cm width by 58cm height. So if these are accurate which I assume they are, you are looking at quiet, sedate fish, as opposed to active swimmers.
Cories will be fine, no problem there. As for the upper fish...hardly know where to begin, there are so many and this is my particular area of interest. Most of my 8 tanks are blackwater species, though the water is not tinted, but with zero GH, zero KH and very acidic pH, that is immaterial. I do use dried oak leaves in some tanks, and all are loaded with wood and/or branches. And sand, very good.
You could do an Amazonian geographic aquascape.
Pencilfish--most of the species in Nannostomus [following Weitzman (2003) all species are presently in this one genus] would be ideal, a couple much less so; I have or have had ten or more species over the years. N. eques swims perpetually at an oblique angle, near the surface, adding some interest. N. mortenthaleri is one of the most beautiful fish in the hobby; closely related to N. marginatus, and was even initially described as a subspecies [Paepke & Arendt (2001)] until Weitzman et al (2001) determined it is a distinct species and named it to honour the owner of the Peruvian collection/exporter firm that discovered the species in the Rio Nanay in 2000.
Hatchetfish--staying only with the smaller species which are all in Carnegiella; these are much less active, almost stationery except when food appears, but still a nice bit of interest right at the surface. The larger species in Thoracocharax and Gasteropelecus are larger, remain below the actual surface, and more lively interacting so less suited here.
Some of the tetras would work. One beauty that is often problematic because its requirement for very soft and acidic water is not met is the false or green neon, Parachierodon simulans. I have a group of these in my smaller (40g) blackwater tank. The closely-related Cardinal Tetra (P. axelrodi) is a bit more red, but the perfectly straight "neon" lateral line of P. simulans makes up for this. These two species are very closely related, their DNA differing only by one chromosome.
The Loreto Tetra (Hyphessobrycon loretoensis) is ideal; rarely available over here, my last two from the original group of 9 acquired some 7 years ago are in this same tank. Nice little tetra. The Ember Tetra (Hyphessobrycon amandae) would add a spot of bright orange (there is a paler more yellow variety not as nice).
Loricaria...Farlowella vitatta is an interesting addition, though it can damage delicate plants like pygmy chain swords but is fine with tougher plants, and wood. The smallest of the Whiptails, Rineloricaria parva, perhaps. I like including one or both of these as they add almost prehistoric interest, and are very peaceful.
A SE Asian geographic aquascape is another optiion. The rasboras will provide fish for this. Some of the smaller and rarer gourami? The cories would not be "authentic" but that doesn't matter if you don't want to be totally geographically-oriented. Except in my 90g which has fish and plants both from three continents I tend to stay geographic but not strictly biotope.
