Home: Mac mini server with external HD for TM backups. Office: TB dock with external drive attached for TM backups. I also have an external SSD with a SuperDuper! clone of my laptop boot drive.
iCloud Drive is not a backup. Let me say that again: iCloud Drive is not a backup. Sure, it can act as one in case of sudden catastrophic hardware failure i.e. you can use it to download all your documents to a new Mac if your old one goes on fire or is stolen, but if you delete a file from your iCloud Drive folder locally it's gone from the cloud and any other synced Macs too.
iCloud Drive is not a backup. Let me say that again: iCloud Drive is not a backup. Sure, it can act as one in case of sudden catastrophic hardware failure i.e. you can use it to download all your documents to a new Mac if your old one goes on fire or is stolen, but if you delete a file from your iCloud Drive folder locally it's gone from the cloud and any other synced Macs too.