Last flannel quilt I made, I washed and dried the flannel twice to get it to shrink as much as possible. Took it out of the dryer on first buzz, shook it out and folded it - did not wrinkle. If you have a serger, I recommend serging the edges first before washing.
I did not starch the flannel and I did not iron it. It was easy to cut, but I only cut one layer at a time. Also, when I was sewing it, the flannel did not shift, it was like it was hugging itself, if that makes sense. You have to be careful and not stretch it.
My son absolutely loves his quilt. When I gave it to him he kept saying "it's so soft!"
I would not use an intricate design - you don't want to stretch it and I honestly would never starch flannel - it would soak too much into it.