Thanks so much for your help!
I am experimenting with the plugin and I think I've (accidentally) made some progress using it, but not nearly as good as your results. My outlines are still pretty light. I don't think I'm understanding exactly what I'm doing with the plugin. Any further pointers you can give? Either way, you've been extremely helpful and I greatly appreciate it!
And yes, I did mean Paint.NET and edited first post
Edit: Nevermind, all I did was add some gray halo outside the white halo, making it appear like it was darker ><