Just to be on the safe side Jim, probably a good idea to seal the back also.
That bark is pretty efficient at holding moisture in. Where did you have it stored? I've got one in similar shape right now and I thought I'd wait til fall before jumping on it. But for yours, I'd give it several months at least under the proper conditions to make sure any use of heat (for straightening or reflexing purposes) doesn't cause any checking.
But as far as Osage is concerned, IMO, the quicker you can get it to a rough bow shape, the quicker it'll dry and thus season faster. Good luck with yours.