What not to worry about at this time
How do I structure my app?
The generators will do it for you.
How do I use my preferred database?
Feathers supports over 20 different databases. Feathers apps are database agnostic for the most part. At worst, it shouldn't take more than 30 minutes to switch your app from one database to another.
Authentication.
Feathers authentication wraps PassportJS so Feathers can do anything Passport does.
How do I use Feathers with React, Angular, Vue?
These are covered in the companion guides.
Is Feathers production ready? Is it scalable?
Yes, and yes. There's detailed information in this post.
Javascript Promises.
Feathers works with both callbacks or Promises. This guide uses Promises as they are prioritized by the Feathers team. We'll be explaining what you need to know about Promises, when you need to know it.