Hi,
Have a look at this example that demonstrate how to make fields dynamic: http://assure.ly/g80MVY.
I think it would be better work with the one field rather than introducing a new one underneath. The user input will be split between the two fields.
You can achieve it using the full event of the first textfield, ie:
textfieldOverflow.presence = "visible";
But I would recommend sticking with one field.
To get the paragraph/other content to move down, the page will need to be set to Flowed content type. See here: http://assure.ly/eSGQMt.
Hope that helps,
Niall