I assume you're using Backblaze to host static assets you're rendering from your compute, and using Cloudflare to front and cache those static assets. You'd also use Backblaze for backups. Most network chatter would remain within your compute, and you'd want Redis, Mongo, Elastic, or Postgres as close to the compute (maybe k8s, maybe VMs, up to you) as possible, while shipping the snapshots to your object store. To your point about bandwidth costs, I recommend Backblaze and Cloudflare because they have an arrangement in that regard [1].

Reliably decouple whenever possible.

[1] https://www.cloudflare.com/bandwidth-alliance/ (Control-F "partners")