Wow. You really need more tanks. I could not have let my severums Nip go to only keep discus. That's why I have 3 tanks. I always said if I could only keep one fish it would be my green severum Nip. So I understand the severum love.
As for Trying to make the perfect tank. There is no such thing we can never be happy with one set up. The tanks are never big enough or there is always that one other fish we must have. It's never ending. This hobby can make people crazy.
You don't have room for another tank??? It's a same to see you let then all go after all that.