Limit Tags display and ad Drop Down Menu

This can be a start…

<?php
$tags = wp_get_post_tags($post_id);
$html="<div class="post_tags">";
$i=1;
foreach ( $tags as $tag ) {
    $tag_link = get_tag_link( $tag->term_id );  
    if($i>3)
    {
        if($i==4)
        {
            $html .= '<ul class="post_tags_menu">';
        }
        $html .= "<li><a href="https://wordpress.stackexchange.com/questions/88264/{$tag_link}" title="{$tag->name} Tag" class="{$tag->slug}">";
        $html .= "{$tag->name}</a><li>";
    }
    else
    {
        $html .= "<a href="https://wordpress.stackexchange.com/questions/88264/{$tag_link}" title="{$tag->name} Tag" class="{$tag->slug}">";
        $html .= "{$tag->name}</a>";
    }
    $i++;
}
if($i>4)
{
    $html .= "</ul>";
}
$html .= '</div>';
echo $html;
?>

How to get post tags
http://codex.wordpress.org/Function_Reference/wp_get_post_tags