Obviously title is clickbait - OP basically deployed a whole set of pods including a db and api layer, basically the entire stack, for each new customer. This is difficulty level "nightmare" and not how most people probably use k8s.

This design has its place and I've built variation of this before, the challenges of doing it this way have nothing to do with k8s IMO. In fact k8s makes it considerably easier to implement which I think is true challenge here - it gives you just enough rope to hang yourself.