Don't wanna spoil too much.
1. There's no story about that in the game yet but we got something planned for that
2. The other rooms will be used, Massage/Nail is planned for part 2 of the game currently
3. There's a window peeping moment we have planned, cool that you found that! but yeah no real plot currently
4. In the version we're working on now we're adding a gallery
5. I don't wanna spoil this, but I've previously mentioned it'll turn into a harem