Shubunkins are basically the same size/shape as comets. In 100 gallon pond, with a good filter/waterfall type set up (for aeration as well as cleaning), you could have 6-7
goldfish easily. The main thing is good filtration and swimming room. My pond is roughly 180 gallons. I think, right now, I probably have about 15-20 goldies in it. I have more than I should, but I also have a larger filter than required and two waterfalls with multiple pools that act as extra filters. Here are a couple pics of my pond at feeding time.