Hi,
What do you mean by "via the HikaShop bank transfer payment plugin" ? Do you mean that you added your link in the "information" area of the bank transfer payment method ? There is no mechanism to have tags in there for order data.
For the final page of the checkout, you could do it instead by making a copy of the file plugins/hikashoppayment/banktransfer/banktransfer_end.php to templates/YOUR_TEMPLATE/hikashoppayment/banktransfer_end.php and then modifying that copy.
In it, you can directly include your HTML and use the PHP variables $this->amount and $this->order_number
For the emails you would have to modify the preload section of the emails via the menu System>Emails.