Hello,

1- “If the post is created with Visual Composer I have no excerpt at all.”:
This happens because you are not supposed to use VC in custom post types. The excerpt will display if you use text editor or any shortcode.
You can change the code to display content text instead of excerpt. For that, go to file \includes\view\blog\loop-grid.php and find these lines:

<div class="text">
    <?php   if($post_format == 'video' || $post_format == 'audio')
             echo codeless_text_limit(get_the_content(), 20);
       else
             echo get_the_excerpt();    
?>

Replace with these:

<div class="text">
    <?php   if($post_format == 'video' || $post_format == 'audio')
             echo codeless_text_limit(get_the_content(), 20);
       else
             echo codeless_text_limit(get_the_content(), 20);    
?>

2- “If the post is a video post – it cuts the excerpt too early”:
The configured number of words to display in case of a video post is 20. You can change that by editing the above file:
Again in these lines:

<div class="text">
    <?php   if($post_format == 'video' || $post_format == 'audio')
             echo codeless_text_limit(get_the_content(), 20);
       else
             echo get_the_excerpt();    
?>

Increase the value (20) to your wish.

Best regards!