Hey Darryl,
its been awhile since i had sausage made, but if i recall correctly i think it may have been 50/50 meat to pork fat. Others may know better. I know it should be cold, almost freezing before the grind.
as far as the other 2 questions, collegen is what we used, but i really don’t remember the size. I don’t know the difference between the casing we used and the alternatives.
if you want pepperettes made, let me know and i’ll pass you the number for larry, the guy that i use. His pepperettes are fantastic.