CIS documentation OES2018 SP2
Yes - standalone CIS server would do for insights.
However, please note that we recommend infra HA setup for production use if you are implementing cloud-tiering. At the moment we don't support converting a standalone CIS server to HA setup.
It is not required to restart the agent service. The agent running on target node can recognize the migrated resource/volumes. Keeping agent configuration consistent on all nodes in a cluster would give uniform experience.