Ralph, if you have a drawknife, rasp, cabinet scraper, and some ambition, you have all you need to make a self bow. A heat gun to remove any twist or to add reflex comes in handy also. Decide on the style of bow you want to make and start removing wood slowly. I usually build my hackberry bows around 1-3/4 to 2" at fades to just past mid limb, then taper to 1/2" tips. Just my preferance. I also heat treat the limbs, but due to the low humidity there it may not be necessary.
I really don't know how much the lower humidity will affect the wood. Your stave has been drying for almost 2 years, if you have a postage scale or something like that, weigh it every few days to see if it looses any weight/moisture. When it stops loosing weight, it should be ready to start floor tillering.
Pearl Drums is one of the best when it comes to hackberry, hopefully he will have some suggestions to help you out.