I chose an instance ran by the same person who owns the mastodon instance I am on, it’s not that popular compared to the big Lemmy instances.
For my mastodon instance I chose one based off of: being on the official list, region, how many people post on that instance in a day (too many posts = too many users), what kind of stuff they post and the rules I have to follow. You could follow the same idea with Lemmy.
For the most part, I ignore the main instance and just look at my subscription feeds through a 3rd party app. So far, nothing bad has occured from being in a small community.
Also, look for posts on Lemmy or Mastodon about updates for a particular instance. My instance is being updated often and is actively geared against the spam bots and ddoss attacks from the past month.
Are you writing a book or are publishing a book? Those are two separate things and if you search up the word authortube on YouTube you’ll get a bunch of people who are looking to publish and not many for fun. And honestly, most of them are not professionals and shouldn’t have their advice be taken.
Writing a draft is not hard and creating ideas isn’t too difficult (the snowflake method is the most popular way to create ideas from a singular idea.) It’s what comes afterwards: revisions (plot, characters, etc.), editing the words, doing those over and over until it is finished.
You don’t need to publish your first manuscript. It’s fine to just write a story or a few for yourself and later on decide if they are ready to go to a publisher or self publish.
Authortubers I like the most are: shaelinwrites, katytastic and Liselle Sambury. The first two both have degrees I think and shaelin is an editor.