No, this size is not on purpose. At its largest, The Menagerie has five women in it! They all adopt an animal identity for their kink/play persona. In chronological order they are; Alice Bolton - Kitten, Mia Russel - Puppy, Elsie Thompson - Piglet, Dove Fowler - Bird, Juliette Hammond - Bear Cub.

Grayson has been polyamorous the entire time he's had romantic and sexual relationships, but when he and Alice began their committed relationship he didn't have any plans to have a harem. When he met Mia he was intrigued by the way she spoke about her play persona and why she enjoyed puppy play as much as she did. Mia is the reason he started the play personas, she asked him to brand her, she's why he even considered trying to pursue other longterm serious relationships.

Every other addition to The Mengarie has been merely through happenstance. He didn't seek the other girls out with the intention of adding them to The Menagerie, it just sort of happened.