I mentioned the use of nitrites if you were going to decide to make a "cooked and cured" type sausage. To keep the fat from breaking, a lower prep temperature is used. This would require using nitrites because the meat is cased and the casing cuts off oxygen. Many types of bacteria thrive in an atmosphere beneath 212 degrees, cut off from oxygen by smoke or casings, and receiving a nutrient sugar present in the meat. The clostridium botulinum bacterium favors all three conditions.4) I don't understand why I would want to use nitrites. I am not opposed to them at all, but I only use them when cold-smoking or aging wursts or salamis. These are fresh bratwurst and do not require nitrites.
Just trying to keep folks healthy.