2) Thats true, but its not leaky abstraction. Clojure never claims to abstract the host away, it embraces it so you can do all low level Java/JS stuff and seemlessly use their libraries without FFIs.
3) You have all Java/JS libs. Most Clojure libs are simply "done", so they get no commits. I don't know of any unmaintend ones.
4) Java is improving? Clojure is mostly done with that already. It was designed long after Java and makes many improvements obsolete.