I have done very little FMQ so I can't tell you anything from experience. I have no recommendation/suggestion about stitch length, etc.
However, I did purchase a book by Sarah Ann Smith, Thread Work Unraveled and she suggested to tape a bottle cap to the foot pedal so that even when you press all the way down your maximum speed is slower. That way you can concentrate on FMQ more and less on speed. I haven't tried it but seems logical.
I have just glanced at the book but it does seem to have good suggestions and is geared towards us that are FMQ challenged. There is a copyright which I will honor. You could google it.
Her website is
http://saraannsmith.com. Hope that helps and good luck.