A: I lengthen my stitch to 2.5-3 when quilting. Piecing is around 2. I release the pressure a bit, otherwise the fabric on top won't always feed evenly. I do a test, but sometimes I do have to change tension when quilting. Usually it's lowering the upper tension by one or more. I usually always have to change tension when I FMQ and that's typically 2 less or so.
B: The top layer has to be pinned, fused with spray products or glue or at least stabilized in some way. All three layers have to be stable. Typically I pin as I don't like fusible batting at all.
Hope this helps.
I've had several WF stop working. They need to be disassembled and repaired. Sometimes the arm comes free or the springs inside are disengaged. Yes, i oil mine occasionally too.