Zener over voltage protection from DC hand crank generator
A linear regulator is inappropriate here.  Use one of the many many buck regulator chips out there.  Pick one that can handle a bit more than the max possible output after the full wave bridge, and you don't have to worry about that part at all.

A buck switcher will be smaller and cheaper than a linear regulator after you include the cost and space of getting rid of the heat.  Even at only 500 mA at 5 V out and 20 V in, a linear regulator will dissipate 7.5 W of heat.  That's not trivial to get rid of, and it's not the worst case either.

Use a buck switcher rated for 40 V, and you're done.