By characins I mean the group of fish known as characins or characidae, which includes the many species we commonly refer to as tetras, pencilfish and hatchetfish.
Many of the tetras do not frequent the upper levels in the tank but prefer the middle to lower levels. Cardinals, emperors, and others like the phantoms, the many Hyphessobrycon species (rosy tetras, roberti tetras, bentosi tetras...), etc. Thinking of upper water level tetras there are the Garnet or Pretty Tetra (Hemigrammus pulcher) and closely related Head & Tail Light Tetra, hatchetfish of course right at the surface, and maybe the Beacon Tetra which is probably the one you mean by red eye. It's been many, many years since I had a group of these, but I think they are upper level fish. You could check the fish profiles section on this forum; I'm not sure, but there may be references to where some of the fish prefer in the water column. Or several other fish database sites.
The gouramis would be more up in the tank, they like floating plants to browse through the roots.
In your 55g with your good weekly maintenance and plants you could have quite a number of different species of small fish like tetras and corys. And like me, with your excellent water parameters the choice is almost endless. Fish others can only dream of will feel right at home in your aquarium with soft slightly acidic water. A good site with photos of many species is Seriously Fish. It's not a forum but a knowledge base so I assume I'm allowed to add a link to the tetra pages: http://www.seriouslyfish.com/kb.php?t=pv&s=2.2