I had assumed that the forms had already gone out in their current form. As it is not too late to redesign the form, I would suggest that you use plain text content controls with the 'allow multiple paragraphs' option set.
For multiple choice questions use content control list boxes.
http://www.gmayor.com/insert_content_control_addin.htm will help you insert the controls, which should have unique tags to make data recovery easier.
http://www.gmayor.com/ExtractDataFromForms.htm will help you recover the returned data from the controls (and it includes a utility for checking the names and tags).
The naming of the files won't matter so much, provided when you save the returned files you don't overwrite existing files with the same names.