I used the Novel template, I think. because I was familiar with it. I tweaked it over the years to way I wanted it.

I don't use the "Notes, Ideas, and Research folders in my Medium file (I deleted them.) But I definitely use them when I am writing my novels.

And I have my Medium writing organized into categories and series. And I have "ideas" documents in all of those.

You are pretty much free to organize it however it works best for you.