You aren't at this time going to get around knowing the jvm infrastructure. That is a requirement. But, you can accomplish a lot without getting too dirty with java itself.

Totally depends on what you want to do.

You need to know a few basic stream/reader concepts to do any I/O, and of course you'll need to know more if you want to use some Java libraries; most of it is easy to pick up as you go. But you can do a lot with pure Clojure.

Java is indispensable in life.

Not even in the form of coffee.

True for at least JVM.

Java is like a fine wine, it gets better with age.