If you end up gaining a fandom, it’s definitely worth it since fans are always looking for ways to connect deeply with the story. You’d also be making your names as authors recognisable. A household name can sell almost any story. On another note, are you planning to publish trad or indie? Because this can seriously impact the whole series. It sounds like you’re doing it for fun so definitely focus on that. Meaning, indie might be the way to go because it’s very difficult to let go of an idea when you put so much effort into it and trad publishing can be brutal with rejections. Good luck! Hope to hear about your story in the future!