Good info above Peter. 30% or better fat to meat works best for me. I also talk to the butcher when I pick up butts and see if they have any good pork fat trimmings that I can use. Otherwise I grab a slap of fatback. Keeping the meat cold while grinding makes the grinding simpler and is also safer. I have a couple of stainless steel mixing bowls that nest together. I put ice in the larger, bottom bowl and then sit the smaller bowl in that one. that helps keep the ground meat cooler, especially if I am going ot be grinding 2 or 3 times.
Another trick is before you start stuffing, pull a little out, make a small patty and fry it up in a skillet. That way you can tell if your spice mix is good or if you need more (obviously it's easier to go lighter in the beginning and ad more if necessary).
Most important thing is just like mixing rubs and smoking meat, have fun and experiment. Worst case is you have to do another batch...darn!
I'm looking forward to hearing how it turns out!
