B. I use plastic sheeting for patterns, ie Visqueen. It's cheap, easy to trace a pattern onto, stiff enough to hold its shape. Can pin, tape, or something together to trial fit.
C. The one hood I've made used no stiffener, but the I sewed the brim separately, and it was stuffed with down. I'd imagine that a flimsy "disposable" cutting board would make for a fine brim stiffener.
D. When you start or finish a stitch line, backstitch over it a couple/few times. In other words, stitch .25 to .5 inch, backstitch, stitch back over, backstitch, stitch back over, backstitch...
E. Button holes, mmm, fun. If you don't have an auto function, set your stitch wide and basically make a bartack, then make sure the needle is in the fabric and lift the presser foot, pivot the fabric 90 degrees, re-set the presser foot, make a tiny short bartack, pivot again for another larger bartack, and once more to close it. Cut a slit in the little box you made.