A: I usually use a Gutterman cotton thread. 50 wt. Since I will be sewing with cotton thread 95% of the time, I set the machines with that consideration.
B:I use 2 layers of quilting cotton. Most people tend to use a thicker material. But, again, this is what I'm going to be using the machine for and it's what I want to look the best.
C: No.