I don't have a Grace frame, but I do use a floor frame for hand quilting.
Leader material is the fabric you attach to the poles. Your top and backing will be attached to the leader fabric - I use pins. The leader material doesn't have to be any special fabric - I used some ugly yardage as leaders on my first frame. It needs to be sturdy enough to hold up to pin basting, but not so heavy you can't pin through it easily.
If you have any Grace specific questions, I bet the Grace Company will be happy to answer any questions.
Good luck!
Janet