I can answer a little of this off the top at 5:25am; more will come.
For my jiaozi, my "traditional" style starts with ground pork (although any ground meat will do). I mix in a good proportion of chopped shrimp meat. (Sorry...I don't measure anything any more unless I'm baking...) I will finely shred a large pile of cabbage or bok choy, put it in a bowl, salt it, and let it sit a while. I will then squeeze the cabbage tightly in my hand to get the extra water out of it, and add it to the meat. I also add a lot of minced garlic, finely chopped green onion, and shredded ginger, and mix it all together thoroughly.
To fill the wrappers, part of the secret is to not overfill the dumplings. A little experimenting will show you the maximum payload you can enclose and get a good seal on the wrapper.
The wrapper has to be firmly sealed when you press it together. Keep a little bowl of water on your prep table...dip a finger in the water and moisten the places where the folded wrapper parts will meet; this helps them "weld together" a little better. Fold the wrapper over and then seal the two sides by pressing them together firmly with your fingers. Then fold the sealed edge into a series of pleats, pressing each pleat sealed with your fingers. A good seal is important...without it, the dumpling will fall apart in the boiling water.
To cook fresh dumplings containing raw meat, bring a large pot of slightly salted water to a boil. Introduce a few of the dumplings...don't cook too many at once or you'll have a sticky mess on your hands. When the water returns to a boil, pour in a little cold water to thoroughly quench the boil. Then stir the water back to a boil, and repeat. The third time the water returns to a boil, the meat will be cooked and the jiaozi are ready to eat.
My dumpling sauce: 2/3 red vinegar, 1/3 soy sauce, a generous dollop of sesame oil, and as much chili paste as I dare, all stirred together.
Note that you can put almost anything inside a jiaozi wrapper, and it's fun to experiment. Chopped smoked sausage and grilled onion was a good combination.
Making, cooking, and eating jiaozi is a great social event. They're labor-intensive to make, but fun when there are lots of hands helping. Enjoy!