A reverse proxy from somewhere like Cloudflare would allow you to host without any router config. Plus, it’d give a little more protection against bots, but it’s not going to block 100% of them.

B2 does charge for API calls: https://www.backblaze.com/cloud-storage/transaction-pricing

Though, it’s not so bad and they give you 2.5k free calls of each paid tier per day.

I really like duplicacy. It’s just a single executable you add to your path, then configure it to back up to basically any remote you want. I don’t even bother to run it in a container since it doesn’t have dependencies. Encrypted, compressed, deduplicated, incremental backups. The algorithm is pretty slick too. It can back up multiple machines to the same repository, and it’ll dedupe across them without any locks required.

Duplicacy CLI is free, and there’s a front-end for a reasonable fee. I think $50 for the first year, then $10 for every subsequent year.

For storage, you can just go with whatever is cheapest/easiest. I use a gdrive I’m paying for regardless for effectively free storage. But if I didn’t have that, Hetzner seems very appealing. I think it’s $4/mo for 1TB? Very reasonable, and you wouldn’t need to worry about api calls or chunk size / file count like you would with S3/B2/StorJ.