An adult ornate will eat adult congos. I tried keeping congo tetras (3" ones) in a 120g 4'x2' with some 6-10" polys, and the senegalus, palmas polli, and delhezi were actively chasing the congos around the tank nipping at them, trying to eat them.
I also once had a 10" endli catch and devour a fast swimming agile lemon fin barb.
If you want long term success, you really do need to look out for larger fish, or a muuuuuch larger tank.
I loved the combo of super red severums with my polys. I had a bright colorful fish to watch, and also my beloved polypterids.
Right now I'm trying archer fish with great success. If you can find nice ones, some archers are very yellow and beautiful.
I know my mix doesn't fit a specific biotope as I would like, but I love my global community. World peace man lol