Backend

if auth is being managed externally, do you still have a user’s table in your database?

Yeah. I've got an internal user ID mapped to the external one + necessary user info. This makes it so I need few external calls and if I ever need to switch auth providers or roll my own it'll be an easy switch.

If you don't, that means an external api request everytime you need to get user info, this will probably slow down your app considerably

Yea I don't want to highly couple user details with accounts

Depends. Do you need personal data for your product? If you don't, the answer is clear. You just go without anything. But normally, you will need something so you will have to save their if in your side so you can link both of them. Thus, my answer would be: it depends.