I’m not sure if you know all about phoenix. Make sure you know how to use Channel API (for WebSockets), because it’s definitely better option than XHR requests.
Make sure writing documentation and tests is not problem for you (maybe even try once TDD for small app).
You should also compare:
Enum > Stream > Flow (library)
There is even ecto API for streaming data from database which makes is really worth especially when you think about huge responses and WebSocket connections.
B(inary) ER(lang) T(erm) is simple and really interesting. Many people miss that just because functions for it are in Erlang core.
Definitely you should know ecto and jason. Those libraries are really often used and are also related to phoenix.
In storage topic next are: :ets + :dets + :mnesia
Look for ecto related libraries for example support for: enums and SQLite
If you want easy project to start on then go to your favorite news page and scrape some data from it (for example last n articles).
Sooner or later you would need to use metaprogramming which is really helpful in some special (not really rare) cases.
Finally I highly recommend scenic and nerves topics.
Possibly related pages:
