Goldfish in a tank that large will be gorgeous!!!

I love goldfish, it's just such a shame they're some of the messiest fish. Because of that I would recommend a set of under-gravel filters, as well as a carbon filter which hangs on the outside (or, they make in-tank ones nowadays which is what I have because it allows the tank to be pushed right up against a wall). You wont need a heater because goldfish like colder temps. (about 74 degrees F)

I would also recommend NOT getting normal gravel. Goldfish were all vaccuum cleaners in another life (-lol-) and they suck everything up, sometimes even swallowing the rocks. So, for their safety and ease of cleaning for you, I'd say to buy the much larger "river rocks". You can usually get those in petstores as well, you just have to look harder.

I used a sheet of aluminum foil as a background on my tank. It was free and it reflects the light and looks really nice. Also, goldfish like peas and oranges. It's neat to watch them eat the orange. Just buy a fresh one, clean it, and cut it into wheels. Let them float in the water and the goldfish will eat the middle of the ring out and swim through it. -lol-

I would put no more than 5 fish in your tank, that way they can get to an impressive size. My favorite are Ryukin goldfish but the panda bear ones can be really neat. There's so much to say about keeping fish! If you have any other questions you can PM me. ^_^ I'd be glad to help. I only mentioned some not-so-common stuff here.