Am I too late to comment on thread? My vintage machines like the thickness of Mettler silk-finish 100% cotton thread. I don't like using thread with poly in it because the poly can coat the surfaces of the needle, bobbin, and bobbin case. I do remember the SM repair guy showing me how to use a Q-tip with oil to dissolve that film from polyester thread around all those parts. I mostly get the largest spools of offwhite and black for all my piecing. If I need colors (for applique) I usually use vintage thread. I unwind the entire exposed surface of thread and then test what's underneath. If it doesn't 'pop' easily when pulled, I'm good to use it.... or I use silk if I have the right color.
Okay, I've put in my 2-cents worth. You all have a great day.