The stew is slightly tart, but you can adjust exactly how tart by using more or less vinegar. I generally use more than soy, but my children like lots of "juice" so I add more soy to taste. Also, I tend to use jarred, minced garlic in place of fresh to save some time.
The original recipe does not include onions or noodles and calls for boiling/simmering all the main ingredients until done and then straining the meat out so that you can brown it and thicken the sauce.
Lungkow Vermicelli is bean thread noodles. I buy them at my local Asian store. 1 bundle is generally 1.3 ounces, but they come in packages of I think 8 bundles. They don't really have a taste on their own, but they soak up the flavor of the stew, and my kids love slurping them up.