a 180 would do you fine for quite awhile, I've said this before, 9 out of 10 of us sell them off before they reach full potential because of many reasons. They get bored, are interested in something else thats coming in, etc. I've always owned a 125 for probably the last 10 years, which is 18" wide,and I've never kept one over 12",and I am just now considering something bigger because I feel as if I finally have the batch I want, 3 Rio Meta Orinos, 4 Guyana Ocellaris, 2 Brokopondo's.
LMAO, i may want something else though "PINIMA" down the road though, you never know.
These fish are very addictive, and so is the hobby, you need to prepare yourself to put some cash in to keep them healthy and well maintenanced if your in it for the long haul.