I think one that is useful here is to understand what is going on at a lower level when you create applications and releases. While you will generally use tools like mix, or rebar3 in the erlang world, to do this, knowing what is going on will definitely help you in the long run, especially if you need to do something the tools don’t do.
Some interesting links are into the Erlang documentation about Applications and Releases. These are at the low level but they do show what is going on. A good book is of course Learn You Some Erlang which has chapters on Applications and Releases. The whole book is very good, even if it is about erlang 
, as it goes through the whole functional/concurrent/fault-tolerant bits in a very good way. There are deeper books if you want more about systems.
Yes, these books are all in Erlang but at this level the mapping erlang<->elixir is pretty straight-forward.
IMAO going from erlang to elixir is easier than going the other way as the erlang language is simpler doesn’t contain so many features as elixir. And no, I have no intention into getting into a pointless argument about this, people get so worked up and lose their sense of humour.
