Okay, can the Phantom Zone Projector be dismantled and re-used as a super suit (as Mark Waid explains)?
Yeah, the zone was used in a similar way by Ruin (Emil Hamilton) during Greg Rucka's abortion of a run on AOS.
Also, can the Phantom Zone be absorbed? I thought it was another dimension.
That, I don't know. Before the formation of the New Earth, there were so many variations of the Zone to the point of being bloody ridiclulous.
Did PC Superman ever use the giant key? Is it possible Rip Hunter and Booster Gold were actually on Earth-1?!
New Earth? My guess is that the classical fortress (with crystal enhancements) replaced the tesseract one that was destroyed during Kal's fight with WW.