According to the Interoperability table the backups and journals of 5.0 can be restored on 2016.2.

Thanks for your thoughts :)

I've got another idea: Why not just copy a full backup file to the new server and do a restore there a day or two before the migration and then during the downtime copy the journals that were created after the backup and restore them.

No need for an extra backup :)

Just have to take care of the journals and not to delete them too often.