Engine Versions

I am a bit confused:

a) I download the source (Say 4.6 Preview) from Github, generate project files, compile UE4.sln and run Development Editor.
b) This pops up an OpenProject/NewProject dialog. I choose New Project and create a C++/Third Person Shooter. A new VS Solution is created and VS opens once again with the new project.
c) I close the first UE4.sln solution. Its included in the new project as a subproject anyways so I have access to all of the Engine code and can debug through it if reqd.
d) I run the game solution and the Editor starts up and I can now create levels, add more code etc.

Questions:

  1. Now lets say 4.6 is released and I download that along with its dependencies. How do I integrate this with my game project? The game project solution includes the old 4.6 Preview Engine solution, how can that be replaced by the new files?
  2. I run VMWare and have the Mac OS running. How do now get the XCode project in sync with all of the above ?
  3. Slightly different question: If I create a Blueprint based game and then add code later on I dont get the Engine project included in the solution. It would be nice to have that. How can this be done ?

Thanks for the help !

Cheers
Sanjit