Elasticsearch from single node to cluster

Hi, I plan to upgrade our ELK setup, where from single server will migrate to new cluster. I plan a 3 server setup for Elastic and have some questions if you could help.

  1. As data will be shared across 3 servers, will be better to have RAID 0 or RAID 1?
  2. SSD or NVME
  3. How to convert single node to cluster for existing ES data?

Thank you.