I have built a few motors over the years. Build it, fill it with fluids, start it and check for leaks, shut it down and change the oil, start it and beat the hell out of it like you normally would.
I don't think taking it easy on a motor is good for it during the first few runs.
Even on my 2-stroke dirt bike, I do this. After a piston and rings it goes right to the woods for a beating.