It is ok to add in hidden form fields to the form to add in this extra info. Once you have the form fields in place and have the values set for them you would make sure to update your update and insert server behaviors to bind the columns in your table with these new form fields.
For the fields you mentioned you should have the following values:
created_by - you can bind this to the existing email field since it is the same value
created_dt - if you want to make it always the time it was created you can just set the value directly in the insert server behavior. The code you would use the for the value of this column would be:
<?php time(); ?>
This will set the value of this form element to be the current timestamp. If you need it to be formated in a particular way you can format the timestamp using the date function in php.
ip_address - you can just set the remote address for this directly in your insert or update server behavior, this is more direct and does not give an opportunity to the user to manipulate this value.
On your update page you would want to set the last updated column to the same value you use for the inserted time column on the insert page.