Hi,
in the list of the types you will find the "Product..." which allows you to display the elements from the "product" table.
By putting the value "product_name", you will display the data from the "product" field "product_name".
If you use a dynamic text, you have to use a tag, like
About the additional fields ; without more details it will be hard to tell you.
But knowing that you can read every data from the database (related to the order and the serial) ; yes you can display content of order/item custom fields.
(Note: item custom field = table "order product").
Regards,