Start off new about 139.2mm dave, so 0.5mm or so (20 thou) potential to take off.
Unless you get lucky, that will be a couple of skims.
I just had mine done, it was unskimmed to start with and not warped, but just to get the face clean and free from the effects of corrosion on the surface round waterways due to an ageing gasket took just over 8 thou (0.2mm)