You dont need any of the defaults like default device pool, ccm group etc, as there has to be another device pool, ccm group before you can delete the default ones. The biggest challenge is to find out if he had modified any service parameters that screws something up. You can reset all service parameters to default from Service parameters page.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.