Characters development in Honey Select Unlimited?

So I bought the HSU from Fakku today, thinking that this game will at least has some development besides being a sandbox. The reception says that girls will randomly visit and how the player chooses to do with them during H scene will affect their future behavior. So far I only see only 1 room, the default room. The only action is call the girl and proceed to H scene. Is that all this game has to offer?

In that same vein, I've seen videos where you can use a wooden horse during spanking. Is that a mod, something that can be unlocked via game progression, or from another iteration of the game?