Realistically I won't have cost-comparisons for a while, as this project is just in the infancy and obviously needs to stabilize/mature first. Although as a qui

Realistically I won't have cost-comparisons for a while, as this project is just in the infancy and obviously needs to stabilize/mature first. Although as a quick summary, your costs should approximately be server(s) that are expensive enough to fit your smallest set of per-user active-data, plus your S3 storage amount, plus S3 API calls (I've made this part a simple options parameter, so you control how often these calls are being made - the more frequent, the more integrity from worst-case disruptions but also more expensive, less frequent and your costs go down). What is worst-case disruption? Everything goes offline simultaneously. User's don't have localstorage fallbacks in their phone/browser so retries rely on the server cache. The server cache is running the default method, not Redis - and then your server crashes or the machine goes under. And finally, of course, there is an S3 outage and you only persisted to 1 region, not multiple regions. I'll get into hairy situations like that in some of my following posts, but too much for here. Yes, you have another good point about query languages. I agree with you very much - somebody else commented about this, check out my reply to muaddirac. Please keep in touch with more questions/comments, or even email me!