Especially beginning out, I would not go with a tank smaller than a 40 gallon breeder tank. 40 gallon breeders are wonderful for there shallow height, great amount of water surface area for oxygen exchange, and manageable on a budget. I would stay away from a 55 gallon, because they are very narrow, and it is hard to stack live rock in them for this reason. If you want a tank that is roughly the same viewing area as a 55 gallon I would go with a 75 gallon or 90 gallon. Over the 75 gallon range you can pick what you want asthetically, but keep in mind how easy it will be to reach down into the tank when needed, some larger tanks can be quite hard to do this (I have to take off my shirt and scrub down before I reach to the bottom of my 220 gallon it's so tall, the water goes past my shoulder)