Sandbox has its merits in doling out character paths and enabling player choice, but it's very rarely done the right way. It's always used to pad time, by adding extra point-to-click and map/menu navigation, waiting to access a specific character's content at a given time, and, not to mention the relationship point/money grind which usually accompanies sandboxes.
People usually want to enjoy a good adult narrative and/or see some adult scenes, pointless and endless clicking and waiting adds nothing to either of those. But there are also some who just like to waste time in mostly empty sandboxes, which I can't relate to, but more power to them.
Sandbox can be done in a simple and easy way, but more often than not, they're used to increase play-time for a skeletal amount of content. And, sandboxes are only worth playing when they have a decent amount of content and more filled locations than empty ones, which doesn't happen until much later in development.
As much as I hate NTR, I despise my time being wasted even more.
Because of the hodgepodge of tags/planned content, I'm not feeling very confident in this project. The dev seems to be playing all sides and trying to please everyone, which we all know, doesn't please anyone. Gives me the feeling, they don't know which direction to take the game. It'd be better to make this a Harem or Romance or NTR/Sharing game, exclusively. That way, whomever the target audience is, they can fully enjoy their preferred content, and people who don't like certain content, can easily skip it.
Either way, best of luck to the dev, hope you find some clarity and inspiration for your project.