Hi Ben,
a lot of questions you have... I understand your thoughts very well because you are going to spend a lot of bucks...
Some fellow members have pointed out that the most important fact is that the watch "talks to your heart".
If you can say "yes" to a special model it will be a pleasure every day you wear it and every time you look at it.
It will be like falling in love with a beautiful girl - you will not be able to take your eyes away from it - at least for the first months, and hopefully for a lifetime
Concerning some of your questions:
I would always go for Patek if I had to chose between several brands!
It is rather difficult to observe prices and " value -keeping" in a rapidly changing market. A watch which is very desirable in our days may be less in 10 years as fashion
and desire change over the times... We have seen this even on Patek models, specially the rectangular vintage models... very high prices in the 90ies and moderate prices now. I am pretty sure that smaller cases and rectangular ones will have their revival some day, but nobody knows how long it will take, it is just a guess...
Don´t see a Patek as a mere investment! They usually keep their value very well, but what is much more important: You will enjoy every second you wear them, and this is most important IMO!
Go for it if it talks to you!
kind regards
Erich