After some trial and error I realised I actually don't want to use Backblaze. These are the reasons:
- It's just too slow at backing up
- It's too expensive for my needs
What I really want to backup is just my photo library and my important source code files.
When I can afford it I'll buy this SSD.
It's then just do a copy paste of ~/Pictures/Photos Library.photoslibrary. I'll also copy paste everything on my desktop (my most important current projects) and everything that forms my scripts library.
If my computer breaks and/or iCloud has issues with my photos I'll still at least have a local backup.