Hi, I discovered your games as I was taking part to the Nanoreno (the year of Tomato Clinic). For sales comparison, have you discussed with other Visual Novel developers? There are all sorts of size and scope for VN and you’ll probably find similar titles to compare with.
If you’re a hobbyist, your objectives may differ from professional teams though, so you must also set your own target figures… or not set them, it depends. I have a few ideas for “games d’auteur” (sorry for the Frenglish) to make and will probably be less concerned by their sales number than with my other games targeting a broader audience. At the same time, if it’s your main type of work, it makes sense to care about how many people you reach… And those willing to pay are probably reached deeply enough that it matters.