I have a Sapphire 830 and it is my work horse! I sew everyday and on w/e up to 14 hours ( my addiction for food and switched to quilting) A few things I have learned along the way:
Thread with the needle in the up position, rewind the bobbin with the needle threaded, clean out your bobbin case frequently, your spring loaded darning/fmq foot may not last long - find the Leah Day you tube video on how to modify any spring loaded foot to fit your machine (wish I found that one sooner and I would have saved $100.00)
If your thread is breaking or shredding during fmq use a larger needle even a generic 110 needle for some threads, using a thinner bobbin thread when fmq Bottom Line, So Fine or Connecting Threads Polyester work best for me.
I hope the things I have learned over 2 years can help someone!