Well if I cancel out an oscar how about a flagtail 4 bala sharks a bichir or eel preferably a fire eel or tire track eel and something else.
My experience with severums is that they are absolutely fine as a solo specimen, no need to shoal them.
Agree that synos can be aggressive.
Ok here it goes my final stock idea for one of them I think,it should work
1 black spotted eel they get about 20 Inches right?
4 bala sharks
1 flagtail or datnoid
1 bristlenone pleco for algae control.