Hey, thanks for giving the game a try ;)
As for your questions:
1 - I hesitate to call this game a 'harem' , because the unspoken rule of this genre is that ALL of the girls present in the game would belong only to the MC. While you can keep all of the main girls to yourself, the side character's purpose are not to be Love Interests for the MC.
2 - There is a gallery planned, the persistent code is already added, so it'll be save compatible.
3 - That individual variable is there so that the player can choose to share some of the girls instead of all of them. Another thing to note is that the MC won't ever 'lose the girls' to someone, it's not Netorare, the sharing is a tool the MC can use to corrupt the girls. (the variable is called ntr because it's a simple and easy to remember name :P). Also, there is a general 'sharing' variable, that if the player refuses, it would turn that content off and hide these options so that the player wouldn't see them anymore.