Author name length character limit?

There’s a filter called get_comment_author that you can hook into to modify a comment author’s appearance.

add_filter( 'get_comment_author', function( $author, $comment_id, $comment ) {

    // limit to first 10 characters
    $author = substr( $author, 0, 10 );

    return $author;
}, 10, 3 );