You ladies are awesome.
I took apart the machine yesterday, thoroughly cleaned out the lint in the bobbin case, changed the bobbin, rethreaded, reinstalled the darning foot and restarted.
This time, I held both threads for the first stitches and... ta-da! I had a few beginner issues and I'm sure my patterns are messy and uneven - but I successfully free-motioned a small quilt. Very proud - and thanks to everyone for the great advice!
The quilt is in the washer right now (hopefully it survives). I didn't know you could make your own bias tape so I used what I had bought at Joann's (double folded quilt bias tape) - but I'm less than impressed with the results. The next one will be made from yardage and sewn by hand.
I think I'm hooked!
Thanks again, everyone - now I'm gonna read through these boards and soak up the knowledge I should have had before I started...