agree on the pattern, squaring a rounded neckline is easy, just remember to make your horizontal line in the middle of the curve, not at the bottom (otherwise you will wind up with a seriously low cut blouse).
The hat is based on a mob cap, which is a giant circle. I'd cut a circle of fabric matching your dress about 24" across, put it over your head, tie a ribbon where you want it to go, then pin & mark all the little gathers that will naturally occur in this process. sew down those gathers to create a reasonably smooth shape (lots of pressing and steaming involved in this step! a dressmakers ham would be handy here) then hem the outer edge. Once sewn, you can starch it & put it over a balloon or something to dry, creating a hat that looks soft, but is in fact rigid.