I have LOTS of wool quilts. They were my mother's favorite to make. She used old wool from jackets, etc. She always put batting and flannel backs. I have used them for years. Loved them the whole time. I wash'em when needed - often a couple of times a winter. Always with cool water and line dry (Or lay flat outside to dry).
I would NOT prewash the flannel
I WOULD put flannel on the back
Depending on the climate, I'd put batting, even if it's realliy thin.
But labels are beyond me. I'd suggest a scripture.