That is a lovely quilt, Sewze!
I would heavily starch the flannel to be used as backing if you are planning to machine quilt. It will help prevent tucks and puckers, plus I think the quilt slides more easily over the bed of the sewing machine.
I'm not sure how starching affects hand quilting. It's probably not necessary to starch backings at all if you are hand quilting, since you want to be able to manipulate the sandwich onto the needle.