Does kubeadm join on the worker nodes configure Pod network, or need to run (3/4) Installing a pod network step on every node?
Reading Using kubeadm to Create a Cluster but not clear what are the worker node specific tasks.
kubeadm join will not configure the pod network. The installing a pod network section that you mention references network middleware that uses Container Networking Interface (CNI). The advantage is that you can deploy special pods that will configure the network in the cluster without having to log in to every node and configure the networking.
For example, this command will deploy pods that will configure the pod networking using Weave Net
kubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')"