Hello, hello!
Delapool was the one who got me interested in Congo Tetras. They happened to pop up at the CAS Auction and when I heard a 12 Congo Tetras, I took the leap!
When I got the bag of them it looked like the size of a Neon Tetra, maybe a bit smaller.
So depending on how large your EN's mouth, you may need to find a good size of fish to buy.
These fish 12 made it to adulthood but a male died and not sure if it was a fight or he got a barb jab by the catfish. He looked perfect, (not ill) with a, thinking maybe puncture wound by his head, which looked like a very small pink red dot.
side note: (Synodontis Lucipinnus previously known as Dwarf S. Petricola more info here
https://www.scotcat.com/articles/article120.htm )
Anyhow, the near dozen fish swim half the time, sit behind the DW and Anubias hanging out with the Glass Cats for a decent part of the day and the rest of the time stay floating mid water very, very slowly moving somewhere else.
This is with decent flow with the FX-5. They eat heartily!
Not having much knowledge about the EN as how they get along with others - I remember a time when Gonzo (is that name right?) Didn't like any tank mates and the newer one and he got along.