If you ever find Sphaerichthys vaillanti, make sure you put them in a separate species tank. They will not do well with the other fishes you have. However, you're probably unlikely to find them due to them being endangered. They might not even be allowed to be collected due to being endangered. Which is kind of stupid in some respects, because if they are left in the wild they will probably become extinct. At least in captivity a few people might breed them.
If you have bigger groups of tetras, they will show up better in the tank. Try to keep barbs and tetras in groups of 10 or more so they can keep each other company and act more naturally.
If you put some Water Sprite (Ceratopteris thallictroides) in the tank, it will float around and make the gouramis and tetras feel more secure. You can also grow the plant in the substrate and it doesn't need anything special to do well, just a bit of light