I made one from red mulberry. Yes, make it a little wider than osage. Yes, remove the sapwood provided you have enough heartwood for a bow. You can leave a sapwood ring if need be.
The bow did fine until I brought it to Mojam in MO 2003. Then it took some additional set.
LOL. I should have known better after having spent 4 months at humid Ft Leonard Wood.
Jawge