1700psi can be used but on a soft limestone or sandstone anything above 800psi can damage the surface, this is why I say you are best to go for something adjustable.
A 90litre vac with pump out is around £600. Get one from Numatic or Tilling Logistics.
In my experience a spinner tool is only used some of the time. I would advise buying a good quality rotary machine with a selection of brushes and a wet vac first. Add the spinner later when you have the volume of work to justify speeding up the process.
These tools are intended for truckmounted carpet cleaners to add tile cleaning while in the home without buying lots of equipment. The reality is anyone who has been working on floors not from the carpet cleaning world doesn't use them.