You have some work ahead of you. If you debarked all staves, you must get all the sapwood off also..NOW. As you take off the sapwood, you must coat it with something like shellac to seal it.(both end and the entire back) If you don't do this, you may end up with a bunch of scrap osage from all the checking that will occur.
The sapwood will let out moisture faster than the heartwood which will make the sapwood start to check. When the sapwood starts to check it will transfer into the heartwood and may turn your nice long stave into a short one before you know it.
You can rough in a bow at just about any time after sapwood is removed and you chase down the rings to about the ring you want for your back, but I would definitely give a green stave a good coating of some kind of sealant to keep it from drying too quickly. IMO
Some of the pro's will chime in here soon and give more input, I am sure. Good luck on your adventure.....Terry