What a wonderful project!
Hopefully we will get some answers for you here, but I would also start talking to your long-arm quilter or decide on one first. They may have specific concerns/reservations.
I have long armed over stuffed applique and did just fine, but it was still quite soft. I've always been terrible about selecting interfacing even when I did garment construction and I think of wonder under as being rather stiff.
And yes -- we will want pictures when you are able! Posting pictures here is an art to itself and some people have more problems than others.