[ithacaartist]

Original black grip scales would be Bakelite. These at least seem to have the proper holes in the back, which should receive grip screws--threaded the same. Heat up a pin red-hot and apply the point to a discreet area on the back. If it produces a little wisp of smoke, they're Bakelite. If it melts a little hole, they're after market plastic. East German VoPo grips are Bakelite, but they have a bulls-eye molded on them.
Yes, the trigger should be blued, not strawed. The X on the frame usually indicates East German, oftentimes reworked for maintenance/rehab, part of its history.
Try downloading our FAQ, which is linked at the top of every page. It's very informative and will likely answer many other questions you might have. (I don't know if it's the same as the one on Jan Still's forum.)
WWII Lugers are reputed to be built of the best steel of any of them. Enjoy yours! Avoid +P, +P+, or NATO ammo. Winchester White Box or Blazer Brass 115 grain FMJ should work fine.