Hi,
1 - I am sorry, the view "listing_price" wasn't the good file.
Please do not post complete files of HikaShop. Don't worry, we already have them 
The view that you want to override/customize is the view "product | show_default".
The price is displaying using:
<span id="hikashop_product_price_main" class="hikashop_product_price_main">
<?php
//LAYOUT listing_price
if ($this->params->get('show_price')) {
$this->row = & $this->element;
$this->setLayout('listing_price');
echo $this->loadTemplate();
}
?>
</span>
And the add to cart is with the quantity:
if(empty ($this->element->characteristics) || $this->params->get('characteristic_display')!='list'){ ?>
<div id="hikashop_product_quantity_main" class="hikashop_product_quantity_main">
<?php
//LAYOUT quantity
$this->row = & $this->element;
$this->ajax = 'if(hikashopCheckChangeForm(\'item\',\'hikashop_product_form\')){ return hikashopModifyQuantity(\'' . $this->row->product_id . '\',field,1' . $form . ',\'cart\'); } else { return false; }';
$this->setLayout('quantity');
echo $this->loadTemplate();
?>
</div>
<?php }
While moving these blocks be careful with the PHP tags, you might need to open/close some.
If you made any kind of error while modifying the view, don't worry. You can simply delete your override in the backend (using the trash icon) and the original view will be restored.
2 - You're right, you can use the minimum price option of the shipping methods in order to create a minimum price restriction.
Kind regards,