Pasta: I've used both bowtie (farfalle) and rotini in this soup with good results. You can also use broken lasagna noodles (don't use the no-boil lasagna noodles). The amount of pasta really depends on how thick and pasta-loaded you want the soup. I usually add the full 12 ounces and then thin the soup out, if needed, at the end with additional broth.
Pressure Release: if you know you are going to let the pressure naturally release all the way and maybe even have the soup sit on warm for a while, I would suggest a cooking time of just 1-2 minutes so the noodles aren't overly soft and mushy.
Tomatoes: you can sub out some of the crushed tomatoes for tomato sauce for a richer, slightly thicker soup.
Pressure Cooker Burn Warning: it's really important to scrape up any bits of cooked meat or other food on the bottom of the pot before pressure cooking. If your pressure cooker gives the burn warning quite often (and seems finicky), you might consider sautéing the meat, onions, carrots in a skillet on the stovetop before adding to the pressure cooker.
Stovetop Directions: in a 6-quart pot over medium heat, cook the sausage or ground beef, onions, carrots and garlic until the meat is no longer pink (break the meat into small pieces as it cooks). Drain any excess grease, if needed. Stir in the crushed tomatoes, basil, oregano, bay leaf, salt, pepper, 6 cups broth and pasta. Bring to a simmer and cook for 15-20 minutes until the pasta is tender, stirring occasionally to prevent sticking. Add additional broth, if needed, to thin. Serve the soup in bowls with spoonfuls of the cheese topping and additional mozzarella or Parmesan cheese on top.