I can't speak about lein or maven, but it is in no way a requirement to use emacs as your editor. In fact, there is really interesting work going on in other editors like Atom with proto-repl[1]. For the web, you can spin up a Gorilla REPL[2] which basically gives you a Jupyter notebook but for Clojure.
[1] https://atom.io/packages/proto-repl [2] http://gorilla-repl.org/