Stocking question

[nd90]

I just bought a firemouth to add to my 90 gallon currently I had a jack dempsey and a Vieja Argentea both are between 5 and 6 inches the firemouth is a little smaller but they seem ok together the argentea picks on the firemouth a little but I am going to make some more hiding spots in the tank I was thinkingabout getting one more firemouth to add to the tank will the 4 fish be ok in a 90 or is this going to cause problems ? My current set up looks like this

 

[AfricanCichlidOwner]

IMO if you provide enough cover they should be fond it seems.