The crumbly stuff just looks like the pith from the middle of the sapling.
Its looks like ash? You will probably find that you will remove the pith when you are tillering unless your after a very heavy bow. If the bow is going to have a none working handle then the pith left can be hidden with a leather grip. It does look like a very nice straight stave so you should be onto a winner
If its fresh cut i would go as far as roughing out the bow to a bow shape leaving the tips wider than needed. The smaller the mass the quicker it will dry. I leave mine in the garage for a week or two them move it indoors. Only start bending it when its dry
I find the best way to stop you taking the stave too far whilst green is to go out and find another stave like this and get that down to rough bow dimensions. This will give you something to do whilst this one is drying.