I'm not sure what were the exact limits, but I definitely recall running into server errors with S3 and the OCI equivalent service — not technically 429s but enough to essentially limit throughput. SQS had 429s, I believe due to number of requests and not messages, but they only support batching at most 10.

I definitely wanted these to "just work" out of the box (and maybe I could've worked more with AWS/OCI given more time), as I wanted to focus on the actual search.

Those are reasonable expectations. I’m very impressed with how it all worked out.