Sharing keys and certificates between SQL Server 2014 server for encrypted backup and restoration

I have six SQL Server 2014 servers. I am not using TDE, Transparent Data Encryption, on any server.

I would like to be able to take an encrypted backup of a database on ANY server and restore that backup to ANY OTHER server.

What actions do I need to take on each server with the service master key, master database key, and certificate? I would like to use the minimum number of keys, certificates, and backup files for these keys and certificates.

What actions do I need to take if I add an additional SQL Server 2014 to the group?

Thank you all. Server Fault and Stack Overflow have helped me many times in the past.