Steps to create Marketer like site

I don't know very well. But why don't you make a backup first by exporting your current settings via GP? Later you can import again.

Hi there,

Marketer is pretty simple - it's all Customizer options.

The header/navigation is using this method: https://docs.generatepress.com/article/navigation-as-a-header/

The blog has the featured image set to the align left: https://docs.generatepress.com/article/adjusting-the-featured-images/

Is there a specific aspect of it you're curious about?

Let me know :)