It is something everybody dealing with AC devices need.
Once I found fairly priced Variac. I’ve put it up in big old rusty chassis previously used for various amplifier projects.

Mains AC goes in front panel switch and neon bulb that signals unit is powered but turned off.
There was no need for turn on signaling because transformers buzz when energized.
After switch there are 2 identical 175VA transformers those have versatile options that I might use in better way or to double the voltage output. 240V primary have 120V central tap, same as 24V-12V-0V secondary coil.
Those are used to isolate grid 240V. I tied them trough 12V line. I don't know will the system have more power if I connect them trough 24V, but lets say isolation is stronger on 12V.
After those two transformers, isolated 240V goes in 2.5A rated regulating transformer.
0-260V goes in bulbs that are switched by 6 contactors, little aux trafo and rotary switch.

I will finished unit photos soon