I'm not clear why you need to see the quilt behind the machine?
An alternative thought...
you could get 11 king size quilts quilted here for 2000 dollars, 22 if you do them double sided like I do. So, many more than that if you make lap/twin size quilts. Just a thought.
I have a 11" harp, but my limit on doing my own quilts is 40 X 40 tops. And on any size harp I have found it much less stressful and easier to use straight line or increasing circles and my walking foot, not free motion wavy lines that require constant shifting.