Are there any special requirements regarding backups when using Security and Encryption, especially with regards to the PGP encryption key from the server?
The macros secure-pass and secure-data are no longer supported and have been removed since version 3.0.0.
Yes, you'll need to back up the PGP encryption key; the PGP encryption key is being stored in the AO_DCA036_GLOBAL_KEY_PAIR table in the database. It is recommended to back up the whole table, then import the table to the new database, to avoid any loss of data.
Encrypted content is already embedded within the body content so that data does not require a separate back up. However, ensure you are not using an instance with deprecated macros below as you will have lots of database tables to backup.