I know nothing about your area, but I have found that I can plant the onions at anytime of year and they will grow.
To store the onions for use I like to pickle them or dehydrate them, using a food drier.
To store the sets for planting, I have kept them in an open container, such as a cardboard box in my pantry. Last fall, my kids put a bunch of sets in a bucket and left them on the back deck. Over the winter they froze repeatedly, but as soon as spring arrived, they began to grow.
I am personally finding that they are harder to kill than to grow.