Questions on Writing a Book

So at the advice of my editor, I’m currently putting together a small, best-of type book, featuring stories that have appeared in the small town seaside newspaper I have been freelancing writing for since it began in 2004. My brain, naturally, keeps telling me I’ve never written a book before and don’t know what I’m doing, no one will want to read it, I have no clue how to publish a book, etc., but I’m taking it one small step at a time and trying not to listen to my brain. I think the best of book would be of interest to the readers of the newspaper, which as I mentioned is a small shore town. I’ve heard Brooke talk about the importance of constraint and narrowing your niche, so would just focusing on those readers as potential book buyers be a smart move?
I never thought about writing a book before, but I’ve made my April goal putting the stories together and how I want them to appear in the book. I’m trusting that each step will somehow organically lead me to the next step. Any good counteracting thoughts you can share with me for when my brain tells me I can’t do it?
Thank you for your time! XO