[qualiteam]

You should look into creating a custom payment method extended from \XLite\Model\Payment\Processor\Offline and use \XLite\Model\Payment\Processor\Check as an example (if you want some data to be entered by customers during checkout).

I believe you should add the extra order fields that will store the data, fill the fields from your offline payment method processor and display the fields in invoices with the help of @ListChild directive.