Go a thicker than 1/8" initially as it's easy to get carried away and ind you are 1/8 on one edge and 1/128" on t'other (unless you've found the only symetrical stave in existence). You don't have to follow a ring, but try to keep it smooth and even with a minimum of violations and those you do have want to be smooth and feathered or angled if possible. I work the sapwood down in stages, get it pretty much right at floor tiller, then keep tiying it up as I progress, so it's pretty clean by the time it's back to brace height and then make sure it's really smooth and clean before any real big flexing. Trying to do it in one hit would drive you nuts.
Like any wood, if you start to feel the edged tools trying to dig in at swirls/knots etc reach for the rasp/file etc.
Enjoy, it's lovely stuff to work,
Del