#1. I start my diagonal quilting from one side near the middle & sew across then sew back across from the other side.
#2. My walking foot DOES back stitch
#3. I always use my walking foot when sewing quilts no matter how thin they are otherwise one layer shifts.
#4. I use a ruler and run my first chalk line and after that I just 'eyeball' the other lines.
my two cents worth. enjoy making the quilt.