You can get a lot done with very basic knowledge. Much of the packages offer example configuration, and as emacs-lisp is self-documenting (through docstrings), being able to read and write basic hooks, functions and setting variables is enough for most configuration.

I personally think after that the challenge becomes emacs, not lisp. For example understanding startup, MIME-types, faces and window/frame rules is a lot to learn - and those are independent of the language