OMG that quilt is gorgeous. I have never seen that pattern. NICE JOB! You need to think about how it is going to look years from now. if you don't quilt the envelopes they will sag, and all go in diff directions. If I were quilting it (and I'm not, just a suggestion) I would quilt 1/4 inch around the inside of envelope (leaving top open) and on down the middle so you can at least have the effect of the envelope, and it will just be split in the middle. it would be 2 halves. like two u shapes. you can still slide something in the envelope.
OMG once again, LOVE IT!
quilter_kjm