My advice here...to achieve this semi-open worldThanks for the feedback!
I would like to comment on the milking thing, to share my view on this (bit of a rant):
I have both a story and "end game" in mind that I want to work towards.
The end game is a "semi open-world" with many girls that can be pursued, but at the core the story revolving around the MC and the main girls.
When you get to the end of a particular character's story arc you should give that character a dating scene where everything you have accomplished with them sexually is available and selectable (Similar to the way a virtual sex DVD works). This would let you focus on sexual content for other characters but allow players to create their own sexual scenes with past conquests when the mood strikes us.
What usually happens late in development is the Dev adds so many characters that none of them get enough scene attention to make anyone happy. There just isn't enough time in the day to make new scenes for everyone. But if you have that one place where you can do whatever is available with them, you can add content to them at your leisure as part of the game and then add that act to the list of acts available on the date.
Similar to your picture gallery only in this case it is sexual positions and acts you can relive.