400w servos should be plenty.
Going smaller is generally not worthwhile as you don't save much $
I have a Delta BE 750W servo as a small lathe spindle motor. The Delta is excellent, documentation is good and in English, and tuning software is available, easy enough to use and works fine on Win10.
Cheaper servos as available but once you put any dollar value on your time it is worth paying for Delta or similar (DMM seems to get decent reviews).
Servos require much more setup and tuning than a stepper and good documentation, and tuning software are essential (unless you have unlimited time and unlimited patience).