I hate to enlist you guys to ID wood but would closer pics help?
Also, I'm ok if it isn't handle worthy - thought it was fortuitous to be right here.
The colors in those stump pictures look amazing. It would make some great looking knife scales with the black streaks.
Sweet birch is an east coast tree. Might be similar, I'm not familiar with it. But this bitter cherry is common here on the west coast. Trees can grow to 45 feet. When it leaves and flowers compare it to this.
http://nativeplantspnw.com/bitter-cherry-prunus-emarginata/
Don't be in a hurry! Air drying rule of thumb in the bone dry winter climate over this way is 1 inch thickness per year and seems to me where you are is much more humid, judging by the mosses and lichens decorating tree trunks in your outdoor shots.
I wouldn't let any sapwood into a handle with cherry, it's considerably softer. From what I've been told, the issue with sapwood inclusion is perhaps moreso that there is a tendency for a split to develop where the sapwood and heartwood meet.
I suppose there is research on this, but fwiw one of my uncles who was a lifetime woodworker told me to coat the ends asap. And that included painting the log ends if not cutting right after felling. So, that's what I do.. . .
Is now when you would paint the ends for storage?. . .