If your feed dogs are down, which they should be for FMQ your stitch length setting is irrelevant. Many say to set it to zero but since the feed dogs aren't engaged I think this may be to save wear and tear for those that can't drop the feed dogs.
Regarding pedal to the medal, I don't agree with that line of thinking and I was vindicated when I read Diane Gaudinski's book on machine quilting. She states she is not sure where that came from about the pedal all the way to the floor. Have it at a speed that feels comfortable to you that is matching the speed you are moving your sandwich under the needle. If you are moving too slow for your machine you will see your stitches are teeny tiny and next to impossible to unpick if you decide you don't like them. If you are moving too fast for what you have your pedal at your stitches will be too big. This is the hardest part of FMQ, getting your pedal foot in harmony with how you are moving the quilt sandwich. It is a constant dance with adjusting your pedal foot speed IMHO.