1 inch wide at the handle will be plenty wide, and your other dimensiions should be ok too. You didn't mention how deep the handle is, but you might start out with something like 1 1/4 inches deep and then thin it down as you start tillering. I've made a couple takedown elbs from ash. Try to tiller your bow so that it bends to the handle. If you have access to some linen it's a good idea to back it before its completely tillered, ( if for no other reason I think the linen makes a cool-looking backing). 67" should be a good length.