My best advice is to read on the subject. Start with Joyce Wilkersons "Clownfishes" as Teeb already suggested. Then move on to some of Frank Hoffs books. Then go back and actually read that thread you previously mentioned. After that, then make the decision how to proceed. IMO, (and not sure how much that is worth) no more than one pair in a system that small (55 gal), and even in the 150 gal, I personally would stick with one pair, but thats me so...like I mentioned....read, read, read....there is a plethora of great information out there. Best of luck