try http://docs.adobe.com/docs/en/cq/5-6-1/wcm/page_publish.html#How%20To%20Restore%20Pages

For security reason trusted_credentials_attribute has been declared deprecated in 5.5 & will support as long you use crx2. However when you upgrade you should not use trusted_credentials_attribute . The going forward option would be develop a custom login module[A] & override isPreAuthenticated meth...

Exclude admin user using package manager filter.

Follow [1] & attach all the logs. [1]  https://docs.adobe.com/docs/en/aem/6-1/deploy/platform/queries-and-indexing.html#Troubleshooting%20indexing%20issues

enable aem with ssl. https://docs.adobe.com/docs/en/cq/5-6-1/deploying/config-ssl.html

need to install couple of hotfix for offloading to work properly. Please file an official support request.

It is expected. If you want to retain the old behaviour configure in felix console.

most of application I have seen does not require sessions to be maintained offcourse you might need to authorize for secured data.   Refer the aem ecommerce implementation for session handling.For bulk upload assets make sure workflow listener are turned off. After upload run the workflow in batches...

Path field does not check for node type. Make sure user trying to verify have access to the node.

using crxdelight acl tab provide permission to node of tab b to group c.