Nice tree.
Get Dean Torges' book, Hunting The Osage Bow. Read it before you cut that tree. He covers it all from picking and felling the tree to applying the finish and everything in between... tools needed and their care, drying boxes, bow design, tillering... An invaluable resource for what you're about to do.
As I made my first selfbow, his book was the only resource I had, I had never even held a selfbow prior, and my first bow still shoots today. I don't take credit for it, rather, see it as a testament to Dean and his book.