please suggest some good books or resources to learn deeply about architectural design and key principals.
You might be interested in this course from Dave which shows you how he builds apps using Elixir:
Programming Phoenix shows you how to build apps using Contexts:
I haven’t read these yet but they might help too:
Also, in case you haven’t read it @sasajuric’s book Elixir in Action shows you how to build Genservers and Supervisors from scratch - which is very helpful for understanding what goes on:
Elixir In Action (Manning)