OK, well I've been looking, and I can't find what event is triggered when a file is added to the table.files or tr.file container.  If somebody can identify that event then a handler can be written to make the numeric field required.

You will need to check the number of files uploaded whenever the fileuploadvalidate event triggers or when the click the delete 'button' on one of the uploaded files. Because of how you are looping them back to the form as they edit it you will also most likely need to check when they first load the page as well. 

We gave our upload button the class name of 'upload'. To figure out how many files were uploaded we counted the number of times the delete 'button' was active.  We also added a hidden field that we use to keep track of the number of files uploaded. This fields class name is checkUpload. We used it for exclusive gateways in the process because we route the form to other individuals if a file was uploaded. Because it has been a while, I'm not sure why when referencing it we went with "$('.checkUpload [vo]').val()" instead of "$('.checkUpload input').val()". 

The field we are setting as required in the function 'setRequiredDocumentWillBeVerified' is a checkbox and because of that the code to set it to required is a bit different but there is commented out code for still there for if it had been a typical input field. 

The class "doseTableField" refers to fields in a table we have that we set them to required (in the first row only) when they have uploaded a file. 

There is also another field that we are hiding and showing based on if a file was uploaded or not. 

/*******************************************************************************/
/*        START: set the fields in the first row of myTable to required        */
/*******************************************************************************/

function setRequiredMyTableFirstRow(isRequired) { 
  /* find the fields that the required attribute is to be modified         */
  /* Each field's input/select                                             */
  /* NOTE: On the layout tab, the fields are set to not required           */
   
  var manufacturerTableFieldSelect = $('.manufacturerTableField select').eq(0);
  var doseTableFieldSelect = $('.doseTableField select').eq(0);  
  var dateTableFieldInput = $('.dateTableField input').eq(0);

  if(isRequired)  {
    /* set the attributes to required */
    manufacturerTableFieldSelect.attr('required', 'True'); 
    doseTableFieldSelect.attr('required', 'True');   
    dateTableFieldInput.attr('required', 'True');  
  } else { 
    /* Hide remove the required attributes  */
    manufacturerTableFieldSelect.removeClass('required').removeAttr('required'); 
    doseTableFieldSelect.removeClass('required').removeAttr('required');   
    dateTableFieldInput.removeClass('required').removeAttr('required'); 
  };  
}; /* END: function setRequiredMyTableFirstRow(isRequired)  */
  
/*******************************************************************************/
/*         END: set the fields in the first row of myTable to required         */
/*******************************************************************************/

/*******************************************************************************/
/*           START: set documentWillBeVerified required/not required           */
/*******************************************************************************/

function setRequiredDocumentWillBeVerified(isRequired) {  
  
  /* find the fields that the required attribute is to be modified         */
  /* Each field's input and the span                                       */
  /* the span holds the asterix that is displayed when required            */
  /* NOTE: On the layout tab, the fields are set to not required           */
  var documentWillBeVerifiedSpan = $('.documentWillBeVerified span.cf-required');
  var documentWillBeVerifiedLabel = $('.documentWillBeVerified .cf-label');
  //var documentWillBeVerifiedInput = $('.documentWillBeVerified input');
  /* used for checkboxes */ 
  var documentWillBeVerifiedInput = $('.documentWillBeVerified span.choice input:checkbox');    
  
  /* Remove span immediately before adding it. It won't remove it if it    */
  /* doesn't exist, but will if it does - you always start with a clean    */
  /* state right before adding it                                          */  
  documentWillBeVerifiedSpan.remove();
  documentWillBeVerifiedLabel.append('<span class="cf-required">*</span>');  
  documentWillBeVerifiedSpan = $('.documentWillBeVerified span.cf-required');     
  
  
  if(isRequired)  {
    documentWillBeVerifiedSpan.show();
    documentWillBeVerifiedInput.attr('required', 'True');     
  } else { 
    /* Hide the asterisks and remove the required attributes  */
    documentWillBeVerifiedSpan.hide();
    documentWillBeVerifiedInput.removeClass('required').removeAttr('required');
  };
}; /* END: function setRequiredDocumentWillBeVerified */
/*******************************************************************************/
/*            END: set documentWillBeVerified required/not required            */
/*******************************************************************************/




$(document).ready(function () {
    if($('.checkUpload [vo]').val() == (0))  {  
       	$('#q132').hide();
    };
});
  
$(document).on("fileuploadvalidate", ".upload", function (e) {
  $('.checkUpload [vo]').val($('.upload .file-del').length);
	if($('.checkUpload [vo]').val() > (0))  {  
       	$('#q132').show();
      	setRequiredDocumentWillBeVerified(true);
      	setRequiredMyTableFirstRow(true);

     };
});

$(document).on("click", ".deleteFileBtn", function (e) {
  $('.checkUpload [vo]').val($('.upload .file-del').length);
      if($('.checkUpload [vo]').val() == (0))  {  
       	$('#q132').hide();
        setRequiredDocumentWillBeVerified(false);
        setRequiredMyTableFirstRow(false);
    };
});

I hope this helps. 

EDIT: 
It should be noted, fileuploadvalidate is not called in preview mode so you will need  to publish in order to test