Don't stress too much about having the "proper" project structure to the point where you might over-engineer or be paralyzed by the thought of doing something wrong.

It's just hard, and even 5+ years of Go experience will not ensure you're creating the optimal packages and structure. It's an art mixed with preferences that become a little easier with time but remain challenging.

I wrote a getting started with Go guide that cover a little about project structure and how to get started with Go.

If you're in writing web applications and maybe even SaaS, I have a course on creating API-first SaaS with Go.