Here's what I got so far:
The symbols on the windows in the drawing room are alchemy symbols; they are sulphur, gold, mercury, silver, and tin
For the butler's room, the year of the cars in the picture frame might have something to do with what you should look up:
Great Britain Rifle Team USA = GBRTUSA (Year car came out might be something important)
TYP-DSN (insert number here): Some sort of ID number (Year of Car ?)
edit - DANG someone got to the alchemy thing before me...
edit 2 - There seems to be an Ouroboros on the lock of the safe that appears to be edited in... More links to alchemy?
edit 3 - Could the letters on the piece of paper in the armory be anagrams? They all form words...