Hello, and welcome to Koko's! My advice is 3-fold and comes from very recent experience (I'm also new).
1. Purchase a 5 gallon bucket if you don't have one, Morton's Pickling salt (it's cheap!) and PraziPro, then read and follow the instructions here, specifically the section "For Fish Purchased from a Questionable Source." This will ensure your fish get off to a great start and will help you avoid all of the problems I had!
2. Change one 5 gallon bucket of water every day until you're able to purchase an API Freshwater Master Kit. Once you get your test kit and can check your water parameters, you may find that you're able to do larger changes less frequently to keep your ammonia, nitrites, and nitrates down until you're tank is cycled. A gravel vacuum is a tremendous help here and is only around $15 at your local fish store.
3. Pick up enough filtration to hit 10 times your tank volume per hour as soon as possible, and then a tank that's at least 48" long when you're able. As someone else said, Petco's dollar per gallon sale is very helpful for tanks up to 55 gallons.
Just a note: I know that goldfish are a bit more expensive on the front end than I originally bargained for, and I hope you're not put off too much by it. I have found that expenses lessen as you get settled, and it's worth it in the end. The "feed me" dance is priceless! Your fish are lovely, and I look forward to watching them grow!
Edited to add: Don't worry about getting a separate tank or tub for the quarantine procedures since all of your fish are new. Also, all of the helpers and moderators here are very kind and really know their stuff...If they tell you something that contradicts anything I've said, go with their advice!