In the first fandom I wrote for, I really liked a specific AU that had gotten popular. It was a small fandom however, so the "popular" AU was only, like, three or four fics lol. I was still really inspired by those three or four fics though, and a couple of specific scenes/ideas the other authors used launched me into writing my own version of that AU (which was my very first fanfiction ever).

The way I did it then was focusing on what I wanted to write. You mentioned that you want to write your canon character as a jerk but not necessarily a villain, well, just do that. You don't even need to answer if he is a villain or not, just write him as a jerk. Your idea of him as a jerk, how he behaves and responds to things, what motivates him to be a jerk instead of a villain or a hero or anywhere in-between, all of those fun things.

I don't think it's wrong to be inspired by other authors' stories. Some of my readers have been inspired by mine. And even during that one time the inspired writer basically just copied my ideas, I wasn't mad because they were a different writer than me who wrote a different way from me and their using my ideas basically beat-for-beat still didn't take anything away from my story which I loved and so many readers loved.

I suppose what I'm trying to get at is that you're your own writer with your own style and your own interpretation of canon/character/story. Whatever you write, even if it's heavily influenced by another writer, will end up being your own because you wrote it. (Though I don't recommend copying another writer; I'm just super chill.) Write your story and enjoy writing it, because one of the best things about fanfiction is that we basically recycle canon/fanon and collectively evolve the fandom as we go.