While it is always better to go with the largest tank you can, A 10 gallon tank from walmart with hood, filter, 1 oz food and 1 oz start right and airpup for $19 more than likely find one in the paper cheaper. Gravel $.99 per bag youll need 3 bags or buy a 5 pounder for $2.99
NO heater is needed for your goldies. (Don't buy your fish there however you will more than likely be dissapointed) This will work fine. Most people think goldies need lots of water and large tanks, really they need lots of Dissolved oxygen.
Two goldies can and will live happily in your tank for a very long time. I would suggest not going with the common or "comet" based gold fish. They will grow too large. Fan tails make great tank mates. They come in a variety of colors including ones called Shubs. They are tri color and really pretty fish.
Goldfish are hearty. Just be sure to cycle your tank prior to buying your fish.
www.ehow.com/how_7595_cycle-new-aquarium.html will help. Also for food, High proteins low fats fresh veggies. here is more on food:
Goldfish need a balanced diet. When choosing a fish food choose one with high protein (48% or better) and low fat (5% or less)
You can supplement their diet with things like Lettuce, mustard greens, turnip greens, collard greens, spinach, peas, endive, Watersprite, seaweed, cukes, kale, chard, broccoli, lima beans, green beans, etc. and feed aquatic plants (e.g. duckweed, azolla, salvenia, etc) or hair algae daily.
For their Carotenoids which are a family of pigments the fish can't make themselves and are obtained as part of the diet. These pigments result in red, yellow and orange colors. Fish have cells called chromataphores. Those cells convert lutein and carotenes into astaxanthin which is the red pigment.
sources include, brine shrimp, krill, spirulina, marigold flowers, paprika, sweet red peppers, yams, carrots, pumpkin
Watermellons and oranges are also good as well as proteins like chicken (chicken livers) beef (livers and parts) and pork as well as worms and bugs.
Good luck and welcome!
EDIT:
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