You can put the default value in with the binding for the field.
Right now for instance the width is set to: <?php echo((isset($_POST["TestimonialImgWidth"]))?$_POST["TestimonialImgWidth"]:""); ?>
Instead set it to: <?php echo((isset($_POST["TestimonialImgWidth"]) && $_POST["TestimonialImgWidth"] != "")?$_POST["TestimonialImgWidth"]:"777"); ?>
Then it will set the value to 777 when it is left blank.
I still don't quite understand the FREE scenario. You have fields to set those values. When would they be used? When would they be ignored and use the FREE value?