Congratulations for this, I think even the basic idea is really good
Are you using some asset for Unity? For Visual Novels I used Naninovel for some time, I combined it with GameMaker because it had visual scripting. Of course, if you are advanced you don't need this, I simply like visual script more then plain C#.
something that I found very useful for facial animations, is to also make a bone for the blush. this way you can use it at any time without depending on a specific expression. also the coloration of the bone (at least in spine allows it) in this way you can customize colors without having to create an image of a specific color, and everything goes via code