Mehsimen
I am only going to say this. My belief is that 2 to 3 girls does not make a Harem. I would say no more than 10. But that would be difficult to balance and keep a good story. So I say 6 because you can balance and maintain the story while still developing a good character for each of his girls. This is where many Harem stories fail. They go for to many girls and don't properly provide for character and relationship development. So I suggest do as many as you feel comfortable developing characters and maintaining the story. Also don't rush if you need a day or two to develop a character or relationship in a chapter take the time. No need to rush it.