This looks decent for what it is. I feel like there are umpteen solutions for easy self-hosted compute (and tbh even a plain Linux VM isn't too bad to manage). The main reason to use a PAAS provider is a managed database with built-in backups.
You can also self host almost any open source service without any fuss, and perform internal networking with telepresence. (For example, if you want to run an internal metabase that is not available on public internet, you can just run `telepresence connect`, and then visit the private instance at metabase.svc.cluster.local).
Canine tries to leverage all the best practices and pre-existing tools that are already out there.
But agreed, business critical databases probably shouldn't belong on Kubernetes.
Regardless, you're going to have a much easier time developing your app if your datastore access latency is submillisecond rather than tens of milliseconds.
So that extra trouble might be worth it...
Also, "small scale" means different things to different people. Given the full topic at hand, I would call it "nano scale". Depending upon your specific schema, you can serve tens of thousands of queries per second with a single server on modern hardware, which is way more than enough for the vast majority of workloads.