My SFE in my fowlr
has not bothered my small clowns and purple psudochromis. They are not known fish eaters.... "KNOWN" Like anything if hungry they may eat a fish. The shrimps are out but mine has not touched a single hermit crab so they would be fine. I don't think they have the crushing power to eat a hermit.
When it gets large it may knock over corals when swimming the tank.
You will need to hand feed the eel because they do not see very well and can not compete for food with the fast fish. I use a feeding tongs to direct feed him in his home.