If you want your users to pay via bank transfer, you cannot automate the validation of the payment as HikaShop cannot have access to your bank account.
So, you will have to validate manually the order in the back end when you receive the funds on your bank account. At that point, you will have the possiblity to send a notification email generated automatically to the user in one click. That way, he will be able to access his order page and download the files attached to the products in the order.