I second exactly what DCM said, if you are a little leary of messing up your osage stave, especially if you paid good money for it and it's your only one, i would suggest building a board bow of hickory, oak, ash, ipe, you name it. The experience you will gain from tillering a board bow will be priceless when you start on your osage bow.
Now if you have a good supply of osage, then just dive right in.
quick note: a bamboo backed osage bow wouldn't be a "selfbow" it would be a, well...bamboo backed osage. A selfbow is exactly how it sounds, one solid piece of wood, all by its "self".