They will love you for the pond pippa! I see so many people make the mistake of keeping goldfish in tanks, and then they wonder why all live in the tanks die... They don't have enough filtration etc, and the buildup of phosphates, nitrite, nitrate and ammonia kills everything, plants included.
With regard to your plants, the more plants the better. Goldfish like to nibble on plants, often destroying them completely. Cabomba is a good plant for goldfish, they will destroy it and eat it, but it is good for them.
Javafern is another good hardy plant, as well as valisneria. Valisneria is available in different kinds, I personally have the valisneria gigantea, and as the name suggests, it grows to gigantic proportions!
Goldfish are bottom feeders, so to keep them healthy and make sure they don't get bloat feed them sinking pellets. If they feed on the surface they ingest to much air while feeding, and as they cannot burp you can imagine the discomfort they are in at that point.
If you do not want to spend more money on plants, which your goldies will destroy, get an air pump with a airstone. You need to make sure that there will be enough oxygen in the water. However, I do suggest getting more plants, it will help your fish survive during a power outtage.
If you have any more questions just shout, I will help where I can to make you and your fishes as happy and long-lived as possible
