Your English is good, don’t worry about it. I personally would not keep severums in a 75 because I personally feel they get to big for a 75 but that’s my just my feelings on it. Eba’s are a great choice for a 75 though. Have you looked at diamond tetras or bleeding heart tetras?
For English not being your first language it’s excellent! 1 Severum might be ok for 75 gallon with some small non cichlid fish like a group of ranbowfish.
Problem is like the user said severums get too big full grown, you could try an appropriate size bottom dweller since severums grow really slow, but it might not fit for life in a couple of years