Crazy idea: if I wanted to implement Clojure on top of the ErlangVM, where should I start?
I would look at retargeting the ClojureScript code generator. Clojure implements a lot of primitives in Java, but ClojureScript is largely written in Clojure and ClojureScript itself so should be easier to port.
Suggestion: Have a look at Lisp Flavoured Erlang [1], a Lisp-2 on top of Erlang/OTP that might be 90% of what you want to achieve. :^) I am sure they are happy for new members of the community!
I would look at retargeting the ClojureScript code generator. Clojure implements a lot of primitives in Java, but ClojureScript is largely written in Clojure and ClojureScript itself so should be easier to port.