Kafka: Is our number of partitions insane?

It's too many. You should ask yourself if you have (or plan to have soon) enough consumer instances to need that many partitions. Then, if you do plan to have 13k consumer instances, what sort of hardware are you running these brokers on such that they would be able to serve that many consumers? That's even before your consider the additional impact of many partitions pre-1.1 https://www.confluent.io/blog/how-to-choose-the-number-of-topicspartitions-in-a-kafka-cluster/

This to me looks like 100 was a round number and seemed future proof. I'd suggest starting at a much lower number per topic (like say 2 or 10) and see if you actually hit scale issues that demand more partitions before trying to jump to expert mode. You can always add more partitions later.