My pond calculator at
http://www.fishpondinfo.com/calc.htm says your ponds would be roughly 748 US gallons if it were all 2 feet deep. Assuming the average depth is half of that, your pond may be about 300-400 gallons. Depending on who you talk to, you'll get a variety of stocking guidelines. In aquariums, they say 10-20 gallons per goldfish which would put 15-20 goldfish in your pond but that would probably be very crowded. Most pond guidelines say 50-100 gallons per goldfish which would be 3 to 8 goldfish which makes more sense. Now, these are as adults. Adult goldfish can easily grow to 12 to 14 inches long. Shubunkins can also grow that large or maybe a few inches smaller. Unless you have them all of one sex, they will spawn. Then, the number of fish is partially out of your control (unless you remove some and find other homes or add predators, etc.). Because they will breed, I would stick to half a dozen goldfish or so unless you lose some to predators. See how well they do. Good luck!