So back to my original question, my new machine running 4.2a 50v steppers and a 3kw spindle I'll be drawing somewhere in the range of 5-6 thousand watts.
even a basic consumer unit will cover those needs easily.

what do you mean by having an isolator in the house? do you mean one line straight from the house's RCD to its own MCB in then going to the shed?

I'm probably not going to attempt it and see if my family are owed any favors, I just want to learn a bit more :)