I would eliminate everything from ‘On your BunnyCDN dashboard, you should create a second pull zone’ up thru the paragraph ending with ‘“standard tier 10$/TB” that I used my for uploads bucket.’
Also, it seems you do need a second CDN pull zone, but it’s not for the backup. I was confused about this, and couldn’t get offsite uploads working until I correctly set up one pull zone to send uploads to BackBlaze (as you outlined) and a second pull zone to pull assets from BackBlaze. See my question about that and the response I got here for more info.