I took the plunge and signed up and now have many questions. Is there a difference between these two types of non-fiction? Can I change formats if I find one is more compatible with my project of editing collection of ancestor letters? Or, which would any one suggest? Many thanks. Loving this app so far!
Do you know what LaTeX is? 
If you don’t know what LaTeX is, you probably don’t need a template for it. It’s one of those kinds of things. 
I don’t want to say you definitely do not, because although LaTeX has a reputation with being primarily of use to the sciences and technical writing, I have enjoyed using it for many years, for many different kinds of texts, including fiction.
Ah, ok. That’s good to know. Thanks for your prompt reply.