Help With Some Advice On a New Story.

So I do need some help from you guys on a few things.

1. A Fan base. I have been writing for almost a decade and I'd like to start building a fan base. What advice could you guys offer to help me out? It'd be very appreciative if even a few of you could help with that and also I'm hoping your advice could help others reading this blog.

2. Changing the atmosphere of any story. My "Hanru Sazuki" story has always been a dark story. Recently I've thought about starting a sixth volume. One major thing about the sixth volume is I wanted to make it less dark and focus more on other elements of what the story was about, which is something I've never done before. Do you guys think it's a bad idea to try and change which elements to exploit in a story? Would changing the elements "ruin" the series or would not changing it make it bland and boring?

3. My next Volume to Hanru Sazuki has a possibility of 3 subjects: Family, Teamwork, or Love. Which subject do you think would be good to write about? This is a decision I'm struggling with.