Redirect first time comments

Since the comment form is generated before the comment is submitted that won’t work too well logically.

The better option is comment_post_redirect filter:

/**
 * Filter the location URI to send the commenter after posting.
 *
 * @since 2.0.5
 *
 * @param string $location The 'redirect_to' URI sent via $_POST.
 * @param object $comment  Comment object.
 */
$location = apply_filters( 'comment_post_redirect', $location, $comment );

You can hook into it, check how many comments user has, and change the URL in $location as necessary.