Pull the expander ball out of the typical FL sizer and you'll find your neck being squeezed down 8-10 thou at least, from fired diameter. The ball pulls it back out to a larger diameter There is usually more than enough to compensate for a couple thou taken off by neck turning. In fact, turning will make the brass last longer because it's being worked less each cycle. Most FL dies are pretty tough on brass.
I don't believe so. The cycle is the difference between fired OD as determined by the chamber and sized OD as determined by the neck section of the die. A thinner piece of brass interacting with the expander ball just shifts some of the cycle away from the expanding portion onto the firing portion of the trip.
I mentioned the thinner brass often working better viewed from a straightness/concentricity viewpoint.