Well, we obviously have paid courses that cover all this, but if you want my personal opinion on package layout, Ben Johnson really has a great article on it here: https://www.gobeyond.dev/packages-as-layers/
To the parent post, there are several articles on Go Beyond[1] that walk through development of an open-source, real-world application called WTF Dial[2]. The source is available on GitHub and you can ask Go application design questions on the Discussions board[3].