How to allow a client to do specialized styling for a single node?
If it is a page with unique structure and no other pages will have same structure, I usually do this by creating an empty page (not a node, just a page - an item in drupal menu system).

You can create a page in your module like so:

function YOUR_MODULE_menu() {
    $items = array();
    $items['your-page-url'] = array(
        'type' =&gt; MENU_NORMAL_ITEM,
        'title' =&gt; t('Page title'),
        'page callback' =&gt; 'your_callback_function_name',
        'access callback' =&gt; TRUE
    );
    return $items;
}

function your_callback_function_name() {
    return '';
}


the code above will provide an empty page. If you need custom page structure for this page you can always declare a template specifically for this page just put:

page--your-page-url.tpl.php


to your theme template folder.

Then you can create blocks for each piece of content and assign them to proper regions. Your users will be able to edit content through blocks edit while all styling and layout tags will be built into template file.