1. sounds like it will be well seasond by now, especially as it has been hewn to rough dimensions. No splits noticable I assume...
2. The sap wood on ash is the back of your bow. As long as the wood is unviolated (ie you haven't cut through the intended back when you removed the bark) it should be okay without backing. But of course that depends on how heavy the draw weight is going to be. Anything above 50# and i'd definately think of backing.
3. see above
4. I have produced several "character" bows from Ash, and as long as you follow the grain you will have a bow that is sound, and unique in appearance.
Happy scraping!!!!
If you do not know where you are going, any road will take you there...