Howdy, Frank
I'm in the midst of doing some neck turning, and have posted a few questions myself as of recently. As for neck "thickness", I've seen some guys run down as thin as eight-thou, but most have complained about split necks, more frequent annealing being needed, and having to handle the cases more gingerly. <this is on bigger stuff --.30-06 and up> I personally would recommend somewhere around minimum of ten, max of...13. I'm doing a variant of a 6PPC now and have the necks at .01225" more or less on the nose. A lot has to do with the over-all quality of the brass--if it's warped like a hooker's conscious, you may be better off turning it to the minimum side of things, as this may aid alignment.
Dave