Hi Fishy06. Feeding them flakes is fine. I guess, like us, they would like variety but i have always kept to the same food for my goldfish and they haven't complained 🙂
Goldfish are cold water species so do not need to be in water that warm but it will not hurt them.
How many goldfish do you have and what size is the aquarium or pond they are in? If you have just filled up a container, added safe start, and several goldfish, then you are going to have problems. Google the aquarium cycle to get an understanding of what is needed. Even with safe start the fish need to be added slowly.
Do you have any plants in there? The fish will like them. Goldfish are really hard on most plants, as they eat them. You should be able to go to your local river and get oxygen weed for them. It needs to be washed very thoroughly before adding it to the tank though.