[X] No one. As much as one may imagine this a momentous occasion, this is, in fact, but a dangerous technical task, on which the fewer people are on the ship, the less trouble an unexpected break can cause.
-[X] We can show the void above to everyone later, once we are sure the vessel won't break under them, and if something does break - we are aware and ready for it.
-[X] All non-essential crew off the ship for the duration of the testing.