Template customization category/listing_div

You can remove the pagination code if you want if you don't use it. You can also keep it for the day when you will have more that 20 categories
That way it would display automatically if needed.

The product listing template is used for products listings.
You don't have to be on a page ctrl=product&task=listing to use it. Anywhere you see a products listing of HikaShop that file is used.

The code is clean don't worry
It's just that you an't load a template from another view like that.
In your category listing menus, you have an associated module which is the one displaying the products listing.
And that's why you have these module variables.

The modules are called directly by HikaShop. They don't have to be published in joomla. They just have to be associated with the menu in the "associated modules" option of the menu.

Indeed by default, a listing of products menu will display the products in the root category. If you want to change that category or tell the system to display all the products even in sub categories, you need to edit the hikashop options of your menu and change the corresponding options 'parent category' and 'sub elements filter'.

There is no need to change the code to display the products. It's just a matter of configuring your menu (and its associated module if it's a category listing menu).

It's normal that the filter template loading code is not working if you're not using the Business edition as this template is only available in the Business edition.

You will have to do a query like that:
$query = 'SELECT a.order_id FROM '.hikashop_table('order').' AS a WHERE a.order_user_id='.(int)hikashop_loadUser();
$this->database->setQuery($query);
$order_ids = $this->database->loadResultArray();
if(!empty($order_ids)){
$filters = array('a.file_ref_id='.$products_id,'a.file_type=\'file\'','a.file_id='.$file_id);
$query = 'SELECT a.*,b.* FROM '.hikashop_table('file').' AS a LEFT JOIN '.hikashop_table('download').' AS b ON b.order_id IN ('.implode(',',$order_ids).') AND a.file_id = b.file_id WHERE '.implode(' AND ',$filters);
$this->database->setQuery($query);
$fileData = $this->database->loadObject();
if(!empty($fileData)){
//display link
}
}

The files are not loaded by default in listings. To get the file_id you first need to load all the files of the product:
$query ='SELECT a.* FROM '.hikashop_table('file').' WHERE file_ref_id = '.$product_id.' AND file_type = \'file\';


Your code is great. After that code you should simplify the code I posted and do something like that:
$filters = array('a.file_ref_id='.$this->product_ids,'a.file_type=\'file\'','a.file_id='.$file_id);
$query = 'SELECT a.* FROM '.hikashop_table('file').' AS a WHERE '.implode(' AND ',$filters);
$this->database->setQuery($query);
$fileData = $this->database->loadObject();

because there is no need to make any link between orders and files via the download table since you already did it with your query.

You're missing the id of the order for which the product was bought in the URL of your download link.

You should change a bit the code of that query

$query = 'SELECT product_id  
    FROM '.hikashop_table('order_product'). 
    ' WHERE order_id IN ( 
        SELECT order_id FROM '.hikashop_table('order')."  
        WHERE order_status = 'confirmed' AND order_user_id = ".(int)hikashop_loadUser().")"; 
$this->database->setQuery($query); 
$this->product_ids = $this->database->loadResultArray();

Ah no, I didn't saw it but you should use the controller order and not the controller product in your URL.
In the order controller, there is also a download task which handles both the file_id and the order_id.

It's normal that the product controller's download task only handle file_id as it is used for free downloads only.