To answer:
I don't think any of his series have been collected as tpb's yet. I could be wrong though.
I dropped it after the second issue. It really jus didn't do anything for me. I've always liked J'onn as a character but the mini just didn't make me care
I think that DC won't give him an ongoing because he just doesn't have the fan base to merit it. Sales of his mini have been less than steller and it seems to me that most writers just don't know what to do with him. He has so much power and there are so many stories you could write about him but most writers keep having him fall back on being lonely about being the last of his kind. I know its central to the character but they really need to come up with new stuff him.