Answering your questions:
a) This language is NOT good for any really low-level stuff like programming realtime hardware systems or low-level processors programming. You should then use pure C or assembler instead. If you are programming other low-level stuff, you could feel comfortable using Luna's textual representation. The visual one gives incredible boost when designing the high-level architecture.
b) At the current stage Luna ships with a very limited standard library, but we will work hard in order to incorporate as many usefull libraries as possible. As you have spotted, Luna is able to directly call Haskell and we also provide foreign C interface, so binding any Haskell library is almost out of the box right now.
c) We are strongly working on this topic. Currently our graphs are able to run in parallel all operations that are not data-dependent in any way. However it does NOT scale well if you're thinking about distributed systems, because it's not easy to determine where to partition your program, so sending data over network will not kill the performance. We will though be working toward addressing it in longer perspective.
Did I answer your question? :)