My experience is that the vast majority of things are out there in the docs, however it does so many things that it takes time to understand it in sufficient depth so as to make significant changes.

The admin is easy; but it's not simple. Behind the simple UI there's a lot of work going on, and a lot of is so that the simple customizations most people work can be done trivially.

Have no shame in making your own templates and views within the admin. That's why it provides those escape hatches.