Oh, I feel your pain. :) Right now, I have two goldfsh tanks; I am seriously thinking of trading the GFs from one tank, and just making it into a tropical mix. It is worse when your friend owns a fish store.. so tempting when she gets new things in. It is nice if you do get a trading relatonship with a store owner; I am not saying that fish should just be throwaway pets to get sick of; but when you are starting out, often there are types out there that you are unaware of, and it can take years of tweaking and trading to get that right tank setup; or you can be like me and risk future-spouse loathing by setting new tanks up every so often! Seriouly, once you get in the swing of it, each tank takes up very little maintenance time, and the then it becomes easier to rationalize new ones! (hey, this won't take up much extra money/time!)
Aleesha, on this forum, has some stellar tank setup; she too would be an awesome advisor!