WP Recent Posts Pro comes with a builtin Shortcode builder. Simply go to the post you want to add the shortcode to and next to the Add Media button you will see Recent Posts Pro. Click on the that button and follow the prompt.
Please let mw know if you have any other questions :)
There currently is not global list of all the shortcode features, but the shortcode builder has settings for all the possible options. So all the possible options in the shortcode are the universe of the shortcode features.
As for the grid display the problem is not the widget but the image you are displaying. You are adding a margin-top: -30px; to the image which is causing it to move up by 30 pixels.
My advice would be to remove that margin-top: -30px; and then everything in your site should line up just fine, but you don’t want to do this add this CSS code to move the grid up by 30 pixels.