Of the three options you've considered, Erlang is clearly the best choice, but why haven't you even considered Java (or any other JVM language)? When it comes to monitoring, profiling or debugging a long-running application, nothing comes close to the JVM. And, needless to mention, it's extremely mature and stable.
A Java memory leak can be solved in a matter of minutes, or – if it's especially complex – in a couple of hours tops. You can take a heap dump and analyze it with Eclipse Memory Analyzer, and if you need allocation stack-traces, you instrument your code with VisualVM. All of this can be done remotely and without stopping the app.
Flight Recorder, which has recently been added to the HostSpot VM, even gives you instrumentation with hardly any performance penalty (though it requires a commercial license if used in production).
Java lets you trade memory for performance. The bigger the heap, the less frequent the young-gen GCs, and the less frequent young-gen GCs, the less garbage you need to collect (because more young objects get to die). So most times when you see large Java heaps that's by choice, as many people prefer paying with memory (which is cheap on servers) for performance. So Java is a "memory hog" only when you want it to run at full speed (and that's true for all generational GC environments). But nothing is stopping you from running "standard" Java with a really small heap; you'd still get better performance than Node or Erlang, and get enjoy all of the excellent tools.
Not knowing it well is a good reason not to use it, though.
I know for a similar project I did, I ruled out Java as I (and my team at the time) were not very productive in it. It mattered, in that instance, but might not in some others. Depends on your teams skill set I guess!
A Java memory leak can be solved in a matter of minutes, or – if it's especially complex – in a couple of hours tops. You can take a heap dump and analyze it with Eclipse Memory Analyzer, and if you need allocation stack-traces, you instrument your code with VisualVM. All of this can be done remotely and without stopping the app.
Flight Recorder, which has recently been added to the HostSpot VM, even gives you instrumentation with hardly any performance penalty (though it requires a commercial license if used in production).