your elephant and knife are fine together. The type of knife you are talking about is not "electric" and will be no problem with mormyrids. When you hear that type of thing, they are talking about the South American knives... totatally different. And, FYI, I keep S.A. knives with mormyrids for years, no problem. Yes, a little aggression if they get close, but not a big deal
in regards to elephant nose: I think in a tank that size you would need a MINIMUM of 10 to make it work. BUT, I know people who have kept 5-6 ok. And your choice of tankmates sounds GREAT.. stick with that AFRICA RIVER theme.... VERY COOL Toyin at Rehoboth has a gazillion fish you could add to that mix. (I like Cogo tetras and red-cap tetras and Elongated Buffalo heads).
I have not ever tried to keep a group of elephant nose, but I tried to keep a group of 7 Mormyrus kannume (dolphins) in a 180 gal planted tank and it was disastrous. highly aggressive, with really complex social structure. Basically there was a pecking order of top- bottom. TOp guy ruled the roost and herded the others into a corner most of the time. At feeding, he ate first... nobody else ate until he was done or he would attack them if he saw them. The others got to eat some, but the lowest fish never ate... so over a period of months, the lowest fish would get beat to hell, ragged and tired and die.. then the next lowest would have the same thing happen to him...
the result was ONE M. Kanumme in the tank, fat and sassy and feeling good about himself after he killed all the others.
So, not sure if elephant nose are this bad, but be cautious.
I will say I have succesfully kept 4-5 DIFFERENT species of mormyrid long term in a 110gal tank (planted, lots of hidign places, lots of other fish) without difficulty. THere was some aggression, but just the territorial "chase you out of my space" type... nothing serious.
So , you might try some other mormyrids with your elephant nose? Example, my M. boulengeri existed ok with my other mormyrids... he was mean, but no harm, no foul. But I know if you try to mix him with other 'boulengeri" they will typically kill each other.
GOOD LUCK. Hope the info helps a bit
