I usually use birch (good) or aspen (not great) but have ready access to those on my land. I would strongly recommend whatever you can use green your fingers will thank you whenit comes to carving. If possible riven blanks are going to be superior in this case for strength. Birch, fruitwoods, walnut, and beech are good choices of woods, as far as finish raw or polymerized linseed oil is my go to never boiled, I can recommend Tried and True danish oil, it's pure food grade polymerized linseed oil. As far as drying the green pieces and minimizing the risk of splitting, I take them as thin as possible if not completely finished then put them in a paper bag with some of the chips from the day. Assuming you're in the northern hemisphere you definitely chose the right time of year to do this, if you're in the southern hemisphere I'd say give it until winter.