I cannot answer all of you questions, but I can answer a few.
1. As far as I have seen there aren't any gotchas that I have come across in an upgrade from 9.0 SP3 to 9.5 SP2.
2. You do not need to add Data Analytics if you plan on going to 9.6. That is included in the installation of 9.6.
I can tell you what I have experienced on my lab cores for your last two questions, but not necessarily real life environments. I have not seen a need to increase CPU or RAM. I also have had good feedback regarding stability of 9.6. As for in a corporate environment, we will have to let others weigh in.
