What happens if I try to download my 30K assets in batches of 30? Would I be rate limited to 30 assets in a period (e.g. a night)? Or would I encounter some other form of rate limiting? Regarding the performance and battery life issues of lots of small requests vs a few large ones, I was under the impression that modern networking protocols like HTTP/3 can efficiently download multiple smaller assets from the same domain. Am I overlooking something?

The only per-widget-instance state is the widget's configuration intent. So if I was in your shoes I would try making my widget use a custom configuration intent, and have a non-editable field of the configuration intent that stored a unique identifier. If you use the UUID class, the ID would be unique.