Have you ever made a bow? If not, or if very few, Id suggest leaving her as is go with it. Reflexed bows, are slightly harder to tiller. As far as backing? I never use one unless I have to. Does your board need one? Bad grain? Pin knots? Anything that says "back me"? If not, Id skip that to. Your 50-60# draw weight sounds good for the bow you laid out providing your not going past 28-29".