You should separate your long-term and near-term storage and treat them as different backup projects. For the near-term that you are backing up weekly and thus

You should separate your long-term and near-term storage and treat them as different backup projects. For the near-term that you are backing up weekly and thus likely need to recover faster and easier in an emergency, borg -> backblaze with your own keys. For the long-term backups that sound more sentimental, the "put lots of 6 TiB HDDs from different manufacturers in safe places" becomes more feasible when you don't have to update it weekly and when it is OK to wait a few days until so you can drive to a relative's house after a disaster. But you also have to test those drives every now and then. I have a bunch of long-term drives at my parents' house a 5 hour flight away, but I visit them every winter and do a test every year. If I needed those today, it might cost me $1000 to drop everything and get on a plane. But if I'm visiting every winter and it isn't really urgent, I can wait. You should think of those kinds of costs too.