the related post query can be found in includes/related-posts.php - the related posts are selected by tags (same tag like current post makes a post related). The query:
asks for random posts but you can set the "orderby" to date or title, etc. too. Corona is optimized for 3 related posts - more or less posts may require major css/html adjustments.
As far as I know there's no way to adjust the text behaviour for "justify". Maybe you can use css attributes like "word-wrap" or "word-break".
Maybe you need to set the image alignment to "left" or "right" instead of "center" or "no alignment" when you insert the image into the content?