Definitely get Adam's book somehow, every now and again they pop up used on popular auction and book retailer sites. But as a short answer to you questions; Cherry can be used for the core as long as the grain is good and there are no knots. But not for bows over 50lbs, if I remember correctly. A SG of .65 or higher would be required for that. You will hopefully get the horn on before you sinew, and only do any tillering after the bow is finished and seasoned, it's all precise measuring up until that point.