Thank you all for your posts. You have given me a lot to think about, and helped me to feel better about where I am 'at'. I feel much more hopeful now (I have taken a 24 hour break from the sewing machine too).
I think the Skillbuilder will be going where UFOs go, and I'll make up some smaller plain sandwiches and just play with them. I am still wishing I could work more intensively on coordinating more complex movement of the fabric with the quality of the stitches, but maybe a bit of meandering will teach me more for now.
Hurrah for lifelong learning and good luck to us all!