Paul,
Craig provided some great resources, you really should take the time to read them. Here are my musings on your thoughts. Take them for what they are worth.....
1. Cure is for flavor....fresh sausage tastes very different from cured sausage
2. You should take the internal temp of hot smoked pork sausage to an internal temperature of at least 155. Beef sausage can be less. The cure helps prevent bacterial growth while the meat is in that danger zone of 70-140. Think of it this way, when smoking you are are creating similar temperature and humidity conditions as an incubator. The sausage is an excellent growth medium that you have mixed the bacteria throughout.
3. Fairly accurate, just really want to stay out of the 70-140 degree range unless it is cured.
4. Cure #1 will dissipate over time. If you use 120+ppm you will be good for 2 weeks. If you are aging for longer periods of time consider using Cure #2 which contains nitrates. These nitrates are converted to nitrites much like a time released capsule. I have a Bresaola which I started curing on October 13th and has been hanging in my curing cabinet since November 8th. The moisture level is right at 79%, and will age probably another 3-4 weeks.
Nitrites and Nitrates are your best friends when it comes to smoked or aged meats. They can be dangerous if not used correctly, but so can my car.
Here is a link to help you determine the amount of cure needed. I like to stay 120-150 for cure #1, and 160-185 for cure#2. Some items which are cured for a very long time, I will go up to 200ppm.
http://www.wedlinydomowe.com/sausage-recipes/cure-calculator
Shannon