What does Minimum Slot Aperature mean?
I would interpret this as the smallest slot they can make is the equivalent of a 0.6mm hole, dragged along the line of the slot. As in, the smallest tool they'll use for a slot is their 0.6mm drill, and they're putting a 0.1mm tolerance on the width of that slot.


  Does this mean that the smallest hole they can make is ~24mils with an annular ring of ~4mils ?


Not necessarily. They may have smaller drill sizes available for vias and non-slot holes.