Your 5196P, is indeed a very beautiful and nice choice as well! I had the opportunity to handle it once again this evening, and thoroughly enjoyed feeling it so much!
As for your questions, I am able to help you in some of them. About the diamond at 6 o'clock, i'm sure you know by now that for all Patek watches that are executed in Platinum since 2000, they all have a 0.02 carat diamond of G or H colour to differentiate them from White Gold or Stainless Steel cases at a glance.
The number Pt 950 represents the purity of the platinum used in the case, that is 95% pure platinum, which is the norm for platinum watches. This is the visible (as in with the naked eye) symbol.
The other diamond shaped emblem which you can see, well the overall shape is diamond shaped, but what is truly important is what is etched INSIDE that emblem. If you use say a 10 times loupe like I do, you can clearly see that there is a set of scales with the word "PT950" between them INSIDE that emblem! This is the hallmark for the metal used in the case, in this situation its platinum. You may notice that to the right of that platinum hallmark there is another symbol with a Saint Bernard dog in it, this is the hallmark for any precious metal made in Switzerland.
As for the PPCe part, i dont know about this, its the 1st time i'V seen it on a Platinum watch of mine, so this might have something to do more with Patek.
Hope i have been of some assistance!
Stephen