integrate with term node count to see number of nodes attached to a term

The node count is already available to the theme function. So if you want this in your site, you can just override this in your theme. Check out this example.

function theme_related_terms_block($terms = array()) {
  $output = '';
  foreach($terms as $term) {
    $output .= sprintf(
      '<a style="font-size: %sem;" href="%s">%s [%d]</a> ', 
      strval(number_format(0.9 + $term['cnt'] * 0.1, 2, '.', '')), 
      url('taxonomy/term/'.$term['tid']), 
      $term['name'],
      $term['cnt']
    );
  }
  
  return $output;
}