I’m sure it’s assumed, but all external graphics files, and camera/audio originals are also backed up. You seem to have the other assets all taken care of. When it comes to backup and archive it becomes a decision of short term, mid-term and long term storage. I don’t really trust long term storage to local drives. I assume those are my short term solution (3 years max with some TLC every 6 months) and those are double copies in two different locations. For longer than that, I make an LTO backup. For a mix of long term is Amazon’s Glacier. Their redundancy and maintenance is awesome so there is no maintenance on my end. There are several GUI’s out there for accessing the archive such as:
https://www.cloudberrylab.com/ppc/new/backup-to-amazon-s3.html?gclid=CKWc-P3y-rgCFcuf4AodqkAArw
And the cost is reasonable on a per program basis. For example, a feature I did all mastered as DNxHD 175, and all audio deliverables, project, trailers, is under 150GB. For that price, it is $0.15/month. It is more expensive to retrieve (like 10x factor), but still quite cheap when pulling from the Glacier archive is really because the drive and the LTO are destroyed.
https://aws.amazon.com/glacier/pricing/
Michael