Welcome from the East Bay in California! My Featherweight uses needle size 14 for piecing, up to 16 for Free Motion Quilting (FMQ) using a special low shank foot that looks like the letter C.
Do a search on this board for "Vintage Machine" and you can connect with a bunch of folks who LOVE Featherweights. They have lots of good information about the care and feeding of this really handy little machine.
I've had mine for about 20 years, found a great sewing machine repair shop who does a really good job on helping keep up the machine, and heartily enjoy using it.
Welcome and good luck!