Get Customer information from order Magento 2

Inside observer,

    $order = $observer->getEvent()->getOrder(); 

    $orderFromFront = $order->getRemoteIp();
    $guestCustomer = $order->getCustomerIsGuest();
    groupId  = $order->getCustomerGroupId();
    $firstname = $order->getCustomerFirstname();
    $lastname = $order->getCustomerMiddlename();
    $lastname = $order->getCustomerLastname();
    $prefix = $order->getCustomerPrefix();
    $suffix = $order->getCustomerSuffix();
    $dob = $order->getCustomerDob();
    $taxvat = $order->getCustomerTaxvat();
    $gender = $order->getCustomerGender();

For shipping address, $order->getShippingAddress()->getData()
And for billing, $order->getBillingAddress()->getData()

You can get all type of customer data using observer.

As per as,magento2 standard,you can inject Sales Collection Factory class,Then Filter that collection by Customer id.

protected $order;
public function __construct(
            \Magento\Sales\Model\Order $order,
        ) {
    $this->_order = $order;
    parent::__construct($context, $data);
}


 public function getCustomAttribute(){
    $order = $this->getParentBlock()->getOrder();
   $orderdetails = $this->order->load( $order->getId());
    return  $orderdetails ->getCustomerId();
  }

or

$order = $this->_objectManager->create('\Magento\Sales\Model\Order')->load($id);
$email = $order->getCustomerId();

But this is not recommended.

Use repository. With $order you can do

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$customer = $objectManager->create('Magento\Customer\Api\CustomerRepositoryInterface')
    ->getById($order->getCustomerId());

$customer is an instance of Magento\Customer\Model\Data\Customer, just call its get() methods to access customer properties.