Welcome! Lots of good people here to help you out.
First, I mounted my Vue on a 10' 6" galvanized fence post, it sits about 9 feet off the ground. I filled the post with concrete for added rigidity and added 3 guide wires to keep it stable in high winds. Click here for some pictures.
http://weather.gladstonefamily.net/site/D3642. They are not designed to mount to a 4x4 post without extra hardware etc to do it that way. I got rid of my 4x4 post after it started to warp and it started messing with the level of the station.
Second, I know there are differences between the two but not significant to really matter one way or the other. The specs for the sensors are identical.
Third, the data logger does not have to stay connected to the pc but I'm not sure why you wouldn't want to.
Fourth, yes, it will work with Vista 32 to my knowledge, not sure about 7 64 bit.