Where exactly do you measure ride heights for setting up the kit. I have no accurate tooling at the moment but am hoping to get some set up gear

It doesn't really matter as long as you use the same place each time. Having said that, most will use the bottom of the chassis rail as it's the easiest place to measure consistently.

Yes, it needs to be a fixed datum. If your dampers and springs are adjustable, measure from the bottom of the wishbone mount to the floor, as long as the floor is level and flat!