Yes, you can import custom field to an order in HikaShop. You just need your custom field as a separate column in your import file. For example, say if you have deliverydate as your custom field then you can import its value like the sample content below where user_email and order_number are needed fields for HikaShop order import.
Do you need to be two reference fields, the email and the order number?
My intention is to add the field of the payment status list with the bank and compare it with the order status. But in the bank list only the order number appears as a reference, the email does not appear.
Yes, you need both the reference fields. The field order_number is to find if there is already an existing order with the same number in database. If not a new order will be created else the existing order will be updated. With email we check if the order is for a valid existing user. Without user_email RO CSVI will not process your order and would show message "Not a valid user with email".