Page-front.tpl.php not working

Make sure to clear your cache in Drupal after major theme changes which include adding files to the theme as above, otherwise your theme may not pick up the new files.

Last I checked, the Devel module was still buggy for D7, but if it has come along then I highly recommend using this along with the devel_themer module, it has a tool that will tell you what exactly to name your theme files for different elements (pages, nodes, fields, etc).

This is a tricky one, but.. your theme hook must match your template name. Weird, but I tested this on my local and it worked once I set it up that way. So.. change your hook_theme() to:

function usuar_theme() {
  return array(
    'usuarbuild' => array(
        'variables' => array('profilesloaded' => array()),
        'template' => 'usuarbuild',
     ),
  );
}

And change your tpl.php file to usuarbuild.tpl.php (or change everything to usertemp). Should work after that.