do you want to have lots of fish? is it a common goldfish? if you don't want lots of fish do what i did and my fish is still alive after being dropped on the floor and going for minutes without air (water) lol
i only bought a starter kit 1st with no fancy nitrates and stuff just plain old rain water, change the water once every week and feed her a flake a night! simple pimple!
really, not being smart but please don't kill any more goldfish before you get used to the way things work