I use 2 1/2 for band or flat lace. I also use my serger so
that takes care of cutting the salvage off because it cuts the selvage off. Yes, I have always been taught to cut the selvage off because of shrinking problems. If the cases are special or from expensive fabric I do the French seams. My Granddaughter who is ADD (in her early 20s) had decided to sew and I am amazed. She has never had an attention span longer than a gnats but give her some frabric and she'll sew for hours. She made her first pair of pillow cases for me. It is so special to spend time with her sewing. My friend bought a new inexpensive machine she didn't like and
gave it to my granddaughter. Needless to say she was thrilled. I have one like it so she uess mine here and has her own at home.