1) See this thread for details on fixing this:
2) It looks like you have some news content pages set in the Content Management section that contain only "<", you will need to remove those from the Power Store CMS.
3) For Authorize.net, you need to set the Login and Transaction Key. None of the settings under the 3D Secure section are required
4) edit the webassist/plugin/cms_templates/footer.php page