Feel free to use any meatballs that you wish. I have a meatball recipe here. Depending on the recipe, the meatballs may fall apart if cooked too briskly, or if you stir them in the pot. It's not the end of the world but if you want to cook them separately (frying them in some olive oil on the stovetop, or baking them in the oven), you can add the cooked meatballs when the soup is done. In place of meatballs, slices of sausage would be nice instead in this soup. I cooked my own beans, starting with 1 cup (200g) dried beans, simmered in plenty of water, until soft. You can use canned beans, drained. Or you can go another route and add a favorite shape of cooked pasta. If using pasta, add it at the end of step #3. To make this soup vegetarian and vegan, use vegetable stock or the cooked bean liquid in place of the chicken stock, and skip the meatballs and cheese added at the end. A few flakes of crushed red pepper would ramp up the flavor. If you save Parmesan rinds for soups, this is the place to use them. Put them in the pot when you add the stock and they'll add a nice richness. (Remove them before serving.)