My question is - what are the current best practices for this specific workflow:
If I understand it right, the main bottleneck is downloading image from docker hub. Is there a way to make this process faster? Anything else I'm missing here?
Have a look at the newly announced Google Container Registry (https://cloud.google.com/tools/container-registry/) in addition to protecting your images with encryption and authentication, it has really excellent download performance world-wide.