Hello Philly. Don't feel so bad. Many of us have been where you are at one point in time. As far as the fish are concerned it really isn't a good idea to mix goldfish (cold water) with tropical fish (warm water). The gold fish alone should actually go into at least a 20g tank. Then for each additional goldfish would require 10g each. If I were in your position I would try to re-home the goldfish and keep the platy's.
A
test kit (
API freshwater) would be your best bet. At the moment your fish are at risk for
ammonia poisoning. Once you get the kit (and I'd suggest soon) you'll be a lot better off. To keep things under control and your fish alive, I would suggest 50% daily or every other day at the very least
water change. Add something like Prime, Amquel + and or Nova Aqua plus. The Amquel + will detoxify the water of ammonia but won't delay the cycle in any way. You'll still get some ammonia readings but they won't be toxic for 24 hours until the next water change. It's going to take time for your tank to cycle.
Hang in there. It will get easier once your tank cycles. Try to keep it fun and best of luck to you and your fish.
Glad you came aboard to Fish Lore!