So at this point, none of the ensigns have seen their cogs yet.  They will see them when they arrive on the Incubator and visit the hangar.

As for Asteria's healing ability, I was thinking that it was a nozzle attached to a hose attached to a tank.  The tank is filled with nanomachines.  Asteria has to be close to the patient cog in order to heal it.  The Asteria has a portion of the Stern Algorithm in itself, which is how it can make the nanomachines repair cogs.  This also gives the Asteria the ability to become sentient in the future. I'll leave it up to you to slowly build up the plot of Asteria (and Nyx) becoming sentient.