We have a few neon zebras, long tail bristlenose plecos and cherry shrimp in our heavily planted 20. A school of cardinals would be pretty. Maybe a couple ottos for algae control.
Every time we add bettas to our 125 gallon planted community tank they just disappear after a few weeks. Don’t know why they can’t thrive there like everybody else. We only try 1 or 2 at a time and it’s a peaceful tank.