What kind of goldfish?
For a fancy (round-bodied), the general stocking rule is 20-30 gallons for the first fish, an extra 10-15 for every additional fish.
For a common, comet or shubunking, 55-75 gallons for the first fish, 20 gallons for each additional. These guys really do better in ponds.
Fancy goldies do best in water 68-75, whilst comets are better in under 72F. They prefer hard water with a neutral to basic pH.
Pellets are best - flaked or floating foods encourage them to gasp at the surface, which can cause swimbladder problems. They like variety, so live food and green plants can also be added to their diet.
For toys, do what you would with a betta - make sure it can't rip their fins. Sand or large tumbled river rocks make the best substrate, as they can swallow gravel.
You need a very high-capacity filter (twice the capacity of the tank) as goldies are messy creatures.
They are social and prefer to be in groups.
They are amazing, beautiful and very rewarding fish, but they are also a big commitment and require an expensive outlay. That being said, once you have everything, maintaining them isn't so pricey. :)
I'd PM KoiMaiden and Olympia and ask them to weigh in, as they are goldie experts in this forum and can correct any mistakes I've made or add extra information for you. :)