I think the handle part should be workable, and look awesome to boot! Serviceberry is a good dense wood, but even pieces that looks straight seem to have some twist, at least for me. you could try splitting it and roughing it out if you want it to dry faster, I've had really good luck with that. If you want to maintain thickness for the handle, try splitting it from both ends and sawing in to the pith at the fades on either side of the handle. the splits will hit the saw cut and stop, and then you can shape the handle however you want. With ocean spray (not sure how serviceberry will react) I've had awesome results just taking off 1/4" or so from the belly side of the handle, and sawing a shallow line along the center, which splits right to the pith as it dries. No harm done to the back and you get to keep your handle an inch thick or more! I'm fairly new at this myself, but thats what i would do with a 7' serviceberry stave, good luck!