Compared to Cataholic, I have a mutli-multi cat house hold and I have 8 males and 3 females. I have never had a real issue introducing a new cat as long as you do it somewhat slowly. This will of course depend on their individual personalities, but you'll know when they are ready to meet. They will be spats and posturing but the cats need to work out a hierarchy between themselves and I've never had to separate animals for fear of serious harm. The more the merrier.