Help needed, advice on dismantelking baring holder/ballscrew

[EddyCurrent]

Gunk might be useful for the cleanup too ?

With regard to the voltage, you need to find out what voltage each component is rated at. The spindle motor and VFD will be the first to look at, the other components will normally have a lower voltage rating but will be supplied via a transformer or power supply so you need to see what the input voltage is for those items. From the sound of "400w 3p" this indicates a control panel taking 400 watts at 3phase voltage (did you confuse this later in your post with "400v 3p" ?) If it is 400 watts then it sounds like a 3phase 415v (or thereabouts) transformer is supplying the cabinet and this could be replaced.
The inverter will have to match the spindle motor or if you want it to work on single phase you might have to replace the inverter and motor. There are other threads in this forum about running spindles and inverters from various voltage sources.