For the update page you will need to set the initial value of the text field to be like this:
$row_WADAProducts['your new column name']
This will ensure that whatever has been set for this value will autopopulate on the update page. You will also need to add this to the detail page where you would like to see this value.
Once you have done that the only thing left to do would be to add in some validation on the form to ensure that the user enters a value, but it seems that since this is an optional field that may not be necessary.