Magento 2 – Get Customer Information from Order

1.) Correct : Well, it largely depends upon the file/situation you are working in. But lot of core templates allow third party extensions to inject their code in a much decent manner, your condition happens to be one of those.

2.) Instead of copying over the entire core file, take a look at the template and layout files for the same. Inside template, you can see that there is a code block as <?php $addtInfoBlock = $this->getProductAdditionalInformationBlock(); ?>.

Now, if you search in corresponding block for the same, you'll see, it is calling the handle additional.product.info from layout, and in layout, it is core/text_list type of block. There you have it. You can simply reference your custom code aiming at this handle and Magento will pick up your information for the display and you won't need to copy over the entire template file to your extension.

Try this approach and see if you get a cleaner extension.

EDIT:

There is not need to do all of that, you can simply call the following function $order->getBillingAddress(); and you'll get all the billing information. This is as long you are using the \Magento\Sales\Api\OrderRepositoryInterface class.

OLD ANSWER

So after a while of search the core code I found this class \Magento\Sales\Api\OrderAddressRepositoryInterface, returns all the billing information.

Here is the implementation in case someone needs it.

use \Magento\Sales\Api\OrderAddressRepositoryInterface;
use \Magento\Framework\Api\SearchCriteriaBuilder;
use \Magento\Sales\Api\OrderRepositoryInterface;

class MyClass 
{
    protected $_orderBilling;
    protected $_searchCriteria;
    protected $_orderCollection;

    public function __construct(OrderRepositoryInterface $orderRepository, OrderAddressRepositoryInterface $orderAddressRepositoryInterface, SearchCriteriaBuilder $criteria) 
    {
        $this->_searchCriteria  = $criteria;
        $this->_orderCollection = $orderRepository;
        $this->_orderAddress    = $orderAddressRepositoryInterface;
    }

    public function myFunctionName()
    {
        $orderFilter = $this->_searchCriteria
            ->addFilter("export_status", 0)
            ->create();

        $orders = $this->_orderCollection
            ->getList($orderFilter)
            ->getItems();

        foreach ($orders as $order) {
            $billingFilter = $this->_searchCriteria
                ->addFilter("parent_id", $order->getData("entity_id"))
                ->create();

            $billing = $this->_orderBilling
                ->getList($billingFilter)
                ->getItems();
        }
    }
}