Those suggestions have completely killed the idea of having even a reasonably enclosed biotope though.
I also believe that if you're going to keep Angels well, in display condition, they're going to need to be the largest mid-water fish in the tank. Perhaps I'm being a little pedantic, but they are almost certainly going to breed if you have more than 3 of them, including both a male and female. If they start picking on something large like a Severum (which have the potential to be incredibly aggressive fish), you're going to run into trouble.
If you want to have a proper shot at this being a biotope (as per the definition, an accurate recreation of a natural environment), focus everything around the Angels. Apistogramma and other Dwarf species, possibly Eartheaters, shoals of Corydoras, schools of Tetra, Pencilfish, Hatchetfish, Loricariinae, etc.
I won't go into exact species I'd keep personally for now, but decide what you want to do. Biotope, or a peaceful cichlid community.