My understanding is that using a VFD as a 3 phase power source doesn't always work well for transformers, contactors and other electrics running off a VFD and it needs to be substantially derated if it is going to handle the start-up serge of the motor. Also the degree of derating depends on the VFD, as many of them these days are derated much more for running off of single phase and normal/heavy duty in constant torque mode. They need to be run in a fixed V/Hz mode. You can direct connect the VFD to the motor and use the VFD low level inputs to run the primary lathe motor. Coolant is usually 3 phase, so may also need to be switched out if you plan to use it. An RPC is a better option if you want a plug and play option, you can buy a control box and pick up an idler motor locally for a lot less than getting/installing an oversized VFD.