First of all, thank you for taking the time to share all your ideas!
Yes, we are thinking of adding some more "generic" encounters such as nurses and teachers mixed with unique and known ones like "Hachishakusama" and "Aka Manto" which is the enemy you encounter in the demo. Currently we're working on more sprites for Shizuka and the interaction with ghosts, since it's our first game on the adult genre, it's quite challenging to decide on which route to take since there's so many options, but we're leaning towards grab type animations.
As for the story, we'll definitely expand as the game progresses!
Now, gameplay. Initial plans are for a camera and a knife, there will be two types of enemies: physical beings that you can defeat with the knife and ghosts that can only be affected by the camera, but we still need to develop more on that. The fire extinguisher and salt ideas are amazing, we'll look into it! Also, Kuon is a great example, I have to play it again after posting this, since I never finished it...
Development may be a little slow from now, since we're still new to Unity and game making in general, but we're looking forward to releasing more stuff as we get it done, thank you :D