> We successfully scaled MongoDB from a few users a day to millions of queries an hour.

Uh, 1 query per second is 60x60x60=216000... Soo, 1 million queries per hour equals 4-5 queries per second.

Soo, that's not even at toy project level. That's extremely low scale, like the smallest possible instance small.

A consumer laptop does 20+k queries/seconds on postgres, mysql etc. a raspberry pi usually still gets 1-3k read queries/s, depending on the used SD card (Or 432 million queries per second).

You're not instilling any kind of confidence quoting numbers like that