Just continue what you are doing. I haven’t read lots of Overlord fanfics, so I don’t know what would be the best to do, but I do know that your story has both the quality(good grammar and plot) and quantity(long chapters),. There is also the fact that you’re making the MC have his own story and he isn’t just some guy that is following Ainz in HIS adventure, therefore making your story unique. I don’t know exactly what readers of Overlord fanfics like, but the way I see it, your originality is a good thing that makes your story different than the others(in a good way).