As we have already discussed the period when the Goldfish are cold is a period of some relaxation, but while there ought not be any maintenance to do, you still need to check them every few days.
You will be looking to make sure they remain healthy, are not suffering any swim bladder or other problems, and are not looking distressed. If they are you may need to separate the affected fish and warm it up so you can treat it. You also need to watch if they start to get too warm. If the temperature hovers around 10C then you are better warming them slightly and feeding again rather than risking the vulnerability that follows from their immune systems closing down but the disease organisms remaining active, which happens at about 10C.
You will also see the fish lose some body mass over the weeks and that will give you a better understanding of the true shape (and therefore merits or de-merits) of the particular fish. If fish look to me losing a lot of body mass – perhaps because they are regularly disturbed or they are active because they are warm but not being fed – then you may need to shorten the cold spell and warm them up to start feeding.
One of the issues we have to watch for is warming and cooling in quick succession as this will upset the Goldfish and make them more vulnerable to disease.
In between all this you can focus on other things and plan the next year!