Forum core module

Im just going over some old core issues and trying to close them.

I will handle your 2nd questions first, as the answer to your 1st question is a bit longer.
A) There are a number of modules that handle notifications, such as Notifications and Watcher. You can even do it manually, with a lot more options, using rules and flags.
B) See below.

I think you will have to get your hands dirty (in code) to handle the forum migration. Whilst the actual node body should be easy to transfer, moving all the comments and keeping the users all correctly assigned will be the hard bit. If you can export from D5 to some sort of text file, there are then various methods and modules to import into D7.

Google will be a great help to find tips/guides/etc, if you havent completed this already. I found and used the code below to create nodes once. It could easily be implemented to parse lines from a text files, and save all the nodes.

define('DRUPAL_ROOT', getcwd());
$_SERVER['REMOTE_ADDR'] = "localhost"; // Necessary if running from command line
require_once DRUPAL_ROOT . '/includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);

$count = '1'; //Starting page
$last = '19'; //Total pages to create from start to this in +1 increments
$prefix = 'SE-'; //prefix the page numbers

while ( $count <= $last ) {


$ptitle = $prefix . sprintf("%02s",$count);
$count = $count + 1;

$node = new stdClass();

$node->type = "book";
node_object_prepare($node);
$node->title = $ptitle;
$node->language = LANGUAGE_NONE;
$node->uid = 1;
$node->body[$node->language][0]['value']   = '';
$node->body[$node->language][0]['format']  = 'filtered_html';
$node->field_vehicle_model[$node->language][0]['tid']  = '4';

$node->book['menu_name'] = 'book-toc-6';
$node->book['plid'] = '639';
$node->book['bid'] = '6';

//$path = 'node_created_on' . date('YmdHis');
//$node->path = array('alias' => $path);

$file_path = drupal_realpath($ptitle.'.jpg');
$file = (object) array(
            'uid' => 1,
            'uri' => $file_path,
            'filemime' => file_get_mimetype($file_path),
            'status' => 1,);
$file = file_copy($file, 'public://');
$node->field_image[$node->language][0] = (array) $file;

if($node = node_submit($node)) { // Prepare node for saving
    node_save($node);
    echo "<li>Node with nid " . $node->nid . " saved!\n</li>";
}

}