Ash steams ok, but works with dry heat much better.
I'd take the bark off asap, as it won't split as it dries. Plus the sooner you get it off, the easier it is. If you leave it until the wood is seasoned, it'll be a pig to remove and you risk digging too deep into the back.
If the sideways bend is a pain in the ass, and you're not keen on straightening, ash works really well turned through 90 degrees. Flip it so that the edge rings are running along the back, and it'll be virtually bulletproof from tension failure. Means you can lay out a straight bow regardless how the grain runs.
If not, and you want to keep the natural back as the bow back, you can lay out a straight bow across a slightly bent stave if you try and minimise the amount of run offs. I've just finished a long narrow ash Warbow that came from a bent stave and I couldn't be bothered to straighten. I just lay out a straight centre line despite the bend and it worked out fine.