Yes, it is possible to have too many cats in a home. The possibility of having a spraying problem increases 10% with the addition of each new cat. Every cat population has its own unique set of dynamics--for some, four is too many, and for others, eight is okay. Much depends upon the personalities of the cats, the size of the home, the way the territory is broken up vertically (with cat trees and perches), as well as horizontally (with different feeding stations and litterbox areas).
The amount of attention given to each cat by the owner is an especially important factor in maintaining a happy and harmonious feline family.
When considering the addition of a new cat to the family, remember that your first responsibility is to the cats you already have.