I'm there you with my own hackberry stave, going for a flatbow, too. It's drying right now after rough shaping it. The limbs are slightly deflexed, like a natural string follow. Looking to steam or heat them up to get rid of that. My stave is 72" long, 2" wide limbs for the most part, then tapering to 1/2", handle is 5" with 2" fades. The limbs are 1" thick off fades and tapering down to 1/2" right now. Won't start final shaping and tillering for a couple of more weeks.
George