@cephie Thanks, that all makes sense.

One thing that I feel may be worth pointing out, is that *most* bog-standard VPS providers (the kind where you pay X per month and get a plan with Y resources) will throttle or suspend your VPS rather than charging overages, so the failure mode for unexpected traffic is "site is down or slow" rather than "unexpected costs". Suddenly charging tons of money is mostly just something the cloudycloud providers like AWS do.

This sort of stuff is often not clearly documented, hence wanting to point it out - but that's not a solution to the rest of your points of course!