There's not that much current going through the wires, so it's not the AWG rating that's most crucial, but the flexing that they have to withstand. Make sure you get finely stranded wire that can take a lot of it, and use cable carriers to limit the radius it has to bend to. The spindle should have a braided shield over the whole bundle, that's grounded only at the VFD end, to avoid creating a ground loop. Make sure the insulation on your wires can take a bit of heat as well; steppers often will run rather hot.
Check the inductance on those motors. Often steppers with a lot of holding torque like those also have a lot of inductance, and require a lot of voltage to overcome it and get up to top speed - which you'll need for cutting wood effectively. Drivers that can tolerate that much voltage tend to be more expensive than ones that can't. The formula is: Square root of the inductance (in mH) times 32 equals optimum voltage to run motor at top speed.