I looked for and couldn't find any answers to basic questions about GKE: - if it is managed k8s does that mean etcd used for storing resources is also fully managed - how updates and backup on etcd is assured - what are the limits? What if I have 50000 different resources, most coming from my CRDs
Do you know any official resources that I can refer to and be sure this is really this way?
Yes, etcd is managed and all that it comes with it. There aren't very specific limits defined in the official docs although 300,000 containers should give you a pretty rough idea. If you have any specific need, for example, hundreds of Deployments, or ConfigMaps, I would contact GCP support with your specific case.