Blog not working properly
If you have issues with the blog settings after following the steps from the Adding Posts article here are some useful information:
The theme doesn't support them in the legacy way because of the post formats blog type. As it can be seen in the online preview of the theme, one post has an image, one a gallery, one a video, and so on. These are post formats which you can set when you create your post. And there is also a place dedicated for post format content in each post (if you select the post to be an image post, there's a custom place to insert the image, and so on..).
The feature images are relevant only in the "latest blog posts" carousel.
Make sure that you select the blog page from your Theme Customizer settings.
Use the blog page template and don't put anything in the WordPress Reading Settings in the place for blog posts.