I believe you can chop it up as you like, but you should wait until after winter.

The inner perimeter of the 'donut' is the oldest part of the crown, and will be the next to die, divided or not. Try to avoid it, and take your divisions from the outer perimeter. Do it in spring, just as the grass is showing it's first signs of life, as Noki suggests.

How many divisions depends on the size clump you have, and the size clumps you want to end up with. You could go as small as just a couple of inches in diameter.

Thanks for the info and instruction it is appreciated.