Glad you liked! Consider leaving a rating. This will help more players to find the game.
As for the content left, it's roughly 50-40% left, depending on the optional quests, activities and other stuff like cutscenes.
To get the special scene in the mansion, get a present from a client based on how well you impressed him. After this, talk with the reception maid and this should be the starting point. Also, I think it won't trigger if you already opened the full gallery via the Patreon code.