Don't have to buy this information, and it's well-documented stuff, too.
http://www.fpl.fs.fed.us/ Download the wood handbook and/or use the search to answer most questions about the behavior of wood.
As far as leaving the pith in endgrain turnings, there are some woods like elm, aspen, or some yellow birch that are virtually bullet-proof when drying, because they grow with reversals in the grain direction. Treat them with less than outright abuse, and you'll survive them. Others like soft maple come with obvious or less-than-obvious checks built in already, and are difficult to survive without extra measures like soaking some CA in the cracks and perhaps sacrifice of a chicken at the dark of the moon. Which is to say dumb luck, regardless of other measures.
Use your knowledge of wood to advantage, and remember that the wood is trying to lose diameter, which means it will lose circumference or split as it does. Put your pith at the bottom of a "U" shape cut as thin as you care so that the length of fiber in continuous contact with other fiber is minimized. Since shrinkage, as politics, is local, you will relieve a lot of the radial stress by allowing the outside to contract into a space rather than itself. I even undercut the bottom of a goblet to take advantage of the space.
Remember that end grain dries at a rate ten times faster than face grain, and keep it open to the air. When I quit leaving things standing on their own base so the top would dry while the underside stayed wet, I gained a much greater rate of success. Doesn't take much, just a couple of parallel sticks with the gap between allowing the bottom to dry at the same rate as the top.
