So what about plants? And substrate? I want to try and keep it as realistic as possible. I have a vague idea of what I'd like it to look like. I want it to be really well planted and be as much about the plants as the fish.
Here's a link to info on plants of different regions. Not much for South America, though. And not many of those are on the easy list! But it might help.
http://www.plantgeek.net/plantguide_cat.php?category=6
A 50 gallon would be nice for a pair of angels. Cories are also South American, they'd fit right in with some of the larger tetras. Angels look great swimming between tall plants.