So I have been asked what thread I use in the bobbin. I always use cotton in the bobbin. I like to use a #50 or #60 weight bobbin thread. I usually use one of three brands, YLI, Aurifil or Coats and Clark, all make really nice colors and good quality thread. But I buy all kinds of thread in all different colors because I match the bobbin color to the top. I have found with my Janome 6600 I rarely have to adjust my tension even with the very thin silk top thread.
I also find that my fusible pieces do not release. I think for a couple of reasons, I am using mostly my own hand dyed fabrics and they don't have any kind of starch or sizing on them so the fusible sticks well. I apply fusible to the whole fabric and then cut out my pieces. But when I do use commercial fabrics I make sure that I have washed the fabric to remove all sizing so that the fusible sticks. I only use WonderUnder fusible web and find that it comes me NO problems and then I make sure that I steam set all my fused pieces after quilting.