limit amount of photos uploaded per cpt post

You can do it like so — refer to the // {comment}:

if (isset($_POST["savepics2"])) {
    // Set max number of files allowed.
    $max_files = 25;

    $attachments = get_children( array( 'post_parent' => $v_Id ) );
    $count = count( $attachments );

    // Check if limit already reached.
    if ($count >= $max_files) {
        echo 'limit reached';
    // If not, then upload the files.
    } else {
        if (!empty($_FILES['vidPix']['tmp_name'][0])) {
            $i = 1;
            $files = $_FILES['vidPix'];

            foreach ($files['name'] as $key => $value) {
                // Check if limit already reached.
                if ( $count >= $max_files ) {
                    echo 'limit reached';
                    break;
                }

                // If not, then upload next file.
                if ($files['name'][$key]) {
                    ...your code here...
                }

                $i++;
                $count++; // increment the count
            }
        }
    }
}