I don't recommend 4 mains transformers in series like that. It's a low-impedance voltage source in the kilovolt range, and that's far too dangerous to be playing around with on the bench, especially for a one-off test -- test setups like this have a tendency to be thrown together quickly and not very safe.
If you *DO* build it from 4-transformers in series, then put them all in a plastic box with 6 x 150k ohm, 1/2W resistors in series at the output, and an easy-to-reach switch to power it on and off. This will limit your exposure to the low-impedance transformers inside, and what's exposed at the output of the box is going to be high-impedance and current-limited to 1 or 2 mA max. The switch at the power-input side will limit your need to reach across the bench (and thus reaching ACROSS the high-voltage power supply) to plug or unplug the device into the wall socket (which are typically at the back of a bench).
A somewhat safer approach might be to wire up a Cockcroft-Walton voltage multiplier. I say "safer" simply because you can drive it from a single 230V mains isolation transformer and limit your low-impedance source to the mains voltage levels (or even less, if you choose to). This way, it won't be able to deliver lethal currents into your body if you accidentally touch it. Dave has done some videos on Cockcroft-Walton voltage multipliers in the past.
Attached is an LTSpice example. You can reduce the output voltage by choosing a mains input transformer with a lower secondary output voltage. You can also remove a multiplier stage too. The combination of input voltage and the number of stages will determine the output voltage.