Setup the new appliance and perform make sure that the basic setup tasks have been performed: Hostname, DNS, partitioning, …
Database Size: /opt/panagenda/pgdata should be the same size at least, but will need more than on the old appliance, since the backup file will be stored there as well. → Link to how How to adjust partitions
Rule of thumb: [new pgdata disk required free] = [old pgdata disk used] *1.3