2. If you are not managing remote cluster using Ambari then its not possible at your end to added the remote hadoop cluster to New Ambari. You need to follow "Ambari Takeover" is a process which can be used to add remote cluster to new Ambari Instance. But it completely depends on which kind of components you have installed and it is usually a tough process to setup Ambari over an existing HDP cluster. But it can be achieved. Similar threads you can find here:
You need to reach Professional services from cloudera team which can help you to migrate remote cluster to new ambari but you need to check possibility of data guarantee before proceeding for this activity.
Your cluster is remote from the standalone Ambari Server running the view and your cluster is not managed by Ambari. IN this case you will need to provide all the configs like NN address, ...etc on your own while creating custom view instances.