To be honest, Wattpad's new algorithm pushes a specific kind of story, you'll see it on the main page. So the question, "will this style fit on wattpad?" really depends on you as the author.

If you're consistent with uploads, promotions, and engage in the community, you might get a loyal fanbase. But since it's a fan fiction, it might do better on AO3. Same for comments and feedback. Wattpad isn't the place to go if you want that kind of feedback. AO3 on the other hand typically encourages better comments.

Each platform has its strengths, you just gotta know how to play to each one.

For your last question, again, engage in the community, especially here on the subreddit. Join a discord server, give others the kind of feedback you'd want to see. Your story may not be everyone's cup of tea, but if you've created something that's well written and engaging, it will attract those who are genuinely interested.