I have 2 emerald corydoras catfish. They do the best in a school of 6 of their own species. I havent decided if I'm adding more emeralds, as the two I have are up in age, or starting a new school of a different species of cory and letting my two be happy with close cousins. I've looked at a few different types and haven't completely decided, but corys are a must.
For dither fish, I have decided on a school of around 12, maybe more, ember tetras. These guys are a cool red orange color and only get about an inch long, so you can stock quite a few in a tank like mine.
For show piece fish I want around 3 to 4 German ram cichlids. They stay small, look awesome and tough like they just got done bench pressing with Halfthor Bjornson... but are actually very peaceful and great community fish. Plus, they do best in a small group instead of by themselves.
Blackwater tanks generally have very soft water, low available nutrients and minerals, lightly if even planted at all, contain driftwood, leaves, seed pods, and have tannin stained water. Carbon is a no go, as it removes the tannins that are purposefully added.
The driftwood, leaves and seeds help to keep the tannins up, or you can make a tea from boiling dry wood or leaves. You can add that tea to the tank to stain the water as needed and for water changes. I also have a bottle of "instant amazon" I got at the freebie table at a fish show. It's just commercial tannin tea consentrate. Usually RODI water is used to keep the water soft and acidic.
I'm not trying to make an exact replica of a blackwater river... I'll have fertilized soil, as all the sandy silty substrates I've found will just cloud my aquarium. The eco complete will give me the look I want and help the few plants I have grow.
This is sort of the look I'd like to accomplish.