Well the fancy goldfish and pleco won't get too big for a 55, but one is cold water and the other is warm. Don't listen to everyone on the internet though since they all think you have the space, time and money to buy and set up a 100+ gallon tank. If anything, get a 55 if you can, then some plants would be cool just be careful since goldfish eat most plants. Another thing, if you can get some good driftwood for the pleco, things like this could work well but I don't know I haven't tried getting it off of Amazon. What is the other fish that isn't the fancy goldfish or the pleco?