What kind of bow do u wanna make? If a short bow I'd remove as much of the sapwood you could and flatten/plane the back down...if making a normal length bow I'd reduce the sapwood to ~1/4" thick following the contours of the back and as close to one ring as possible(but a few subtle violations are fine)and rawhide back it...ive done sinew,rawhide,and hickory backed erc bows,and with your experience level id make it as long as you possibly can and go the rawhide route
I'm actually in the process of shooting in a rawhide backed ERC longbow this weekend and they are pleasant shooters and super light in the hand ...got any pics of your stave? That will help
Knots can be an issue with the stuff FYI as well,and could affect the best possible layout of your stave