My parents-in-law have 6 cats and in my opinion that's too much (I won't be the one telling them ). One of the cats sprays around the house, I had the unpleasant honour of getting my share of it.
Of course it varies what's too many for different people, some might be comfortable with 10 cats and some with only 1. Depends on the person. Never mind what others say, just take care of as many cats as you can!