I’d suggest the best way to go about this is to base your modifications on an existing layout file. For instance, content-grid_2_cols.php.
If you open it, you can see the layout is made with the Bootstrap framework. This means you can control the width a post occupies by altering the classes. After that, you may also like to center the textual parts of the posts. And use larger thumbnail sizes.
Please mind that such modifications should be made in a child theme so that your changes don’t get overwritten during theme updates.
FYI: when I was working on this design, I did not create a list view because I did not really like the way it was coming along with the style of the theme.