I'm speaking from my own personal experience with posting stuff online of my own writing. Anything I wrote that was fanfic got and still gets 10x more views and likes and hearts than anything I write that is original. I've even tested the hypothesis with smut writings, fanfic and not, of similar writing quality and it's the same. I can get into a rant about it, but that's my own personal experience with the internet. "Hates original, loves fanfics." Also note that if you're planning to publish the original work on Ao3, you'll be met with push back in viewership (one site where I did my stat testing oddly enough). There was a thread here a while ago where someone argued that Ao3's policies / ToS now are written to not allow for original work at all on there, but upon reading myself I couldn't find the clause they were thinking meant that - and when asked here on the forum - I don't recall if they were able to provide the exact legal clause or statement that stated Ao3's position (either way) on original work being posted there.
As for, monetary success - Fifty Shades has, what two movies, out now plus large amounts of books sold and even the joke readings on youtube point to it's "success" if only in infamy. But it's enough attention on any one thing to get it movies. Can't say that went that well for other book serie's : The Black Cauldron, Tales from the Earthsea, and Howl's Moving Castle. Of those thing, you're like to think Howl's is actually good - well not if you've read the books. It's much like any book made into a movie
Such is reality sadly.
As for honestly - write whatever the damn well you feel like. If you like the core ideas and thoughts that your fanfic stirred up, then see them through and follow them. I am not ashamed to admit some of my earliest honest efforts into writing a longer story with meaning came in the form of a fanfic. I ended up with a large cast of characters, a deep world, and parallel worlds - if you look at my novel today you'd think the only thing I kept was my crappy sense of humor and the idea of parallel worlds. And that's not a fanfic rewrite. It's just writing what I wanted to and the stuff organically formed its way into the story. But I don't plan at all
Lots of my stuff are feeling "I want it to go like this" so if this character feels like this right now, then later they should be able to feel "this"? laughs nervously I hope that makes sense.